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00 ANATOMY 

V FOR STUDENTS THIRD EDITION 

I'M Ik r li> y . I 












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Drake, Vogl & Mitchell 
2014. ISBN: 978-0-7020-5131-9 



Gray’s Anatomy for Students 
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C/J 

>1 


o 


Anatomy 

for students 



Richard L. Drake, PhD, FAAA 

Director of Anatomy 
Professor of Surgery 

Cleveland Clinic Lerner College of Medicine 
Case Western Reserve University 
Cleveland, Ohio 

A. Wayne Vogl, PhD, FAAA 

Professor of Anatomy and Cell Biology 
Department of Cellular and Physiological Sciences 
Faculty of Medicine 
University of British Columbia 
Vancouver, British Columbia, Canada 

Adam W. M. Mitchell, MB BS, FRCS, FRCR 

Consultant Radiologist 
Chelsea and Westminster Hospital 
Honorary Senior Lecturer Imperial College 
London, United Kingdom 

Illustrations by 

Richard Tibbitts and Paul Richardson 

Photographs by 

Ansell Horn 





ELSEVIER 









CHURCHILL 

LIVINGSTONE 


ELSEVIER 


1600 John F. Kennedy Blvd. 
Ste. 1800 

Philadelphia, PA 19103-2899 


GRAY’S ANATOMY FOR STUDENTS, THIRD EDITION 
International Edition 


ISBN: 978-0-7020-5131-9 
ISBN: 978-0-7020-5132-6 


Copyright © 2015, 2010, 2005 by Churchill Livingstone, an imprint of Elsevier Inc. 

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, 
including photocopying, recording, or any information storage and retrieval system, without permission in writing from 
the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our 
arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be 
found at our website: www.elsevier.com/permissions. 

This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as 
may be noted herein). 

Notices 

Knowledge and best practice in this field are constantly changing. As new research and experience broaden our 
understanding, changes in research methods, professional practices, or medical treatment may become necessary. 
Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any 
information, methods, compounds, or experiments described herein. In using such information or methods they should 
be mindful of their own safety and the safety of others, including parties for whom they have a professional 
responsibility. 

With respect to any drug or pharmaceutical products identified, readers are advised to check the most current 
information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify 
the recommended dose or formula, the method and duration of administration, and contraindications. It is the 
responsibility of practitioners, relying on their own experience and knowledge of their patients, to make diagnoses, to 
determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions. 

To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for 
any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any 
use or operation of any methods, products, instructions, or ideas contained in the material herein. 

ISBN: 978-0-7020-5131-9 


VP Global Medical Education Content: Madelene Hyde 
Senior Manager, Content Development: Rebecca Gruliow 
Publishing Services Manager: Patricia Tannian 
Senior Project Manager: John Casey 
Design Direction: Lou Forgione 

Printed in Canada 

Last digit is the print number: 987654321 


Acknowledgments 


First, we would like to collectively thank those who agreed 
to examine earlier drafts of the book—anatomists, edu¬ 
cators, and student members of the editorial review board 
from around the world. Your input was invaluable. 

We’d also like to thank Richard Tibbitts and Paul Rich¬ 
ardson for their skill in turning our visual ideas into a 
reality that is not only a foundation for the acquisition of 
anatomical knowledge, but also is beautiful. 

Thanks must also go to Madelene Hyde, Bill Schmitt, 
Rebecca Gruliow, John Casey, and all the team at Elsevier 
for guiding us through the preparation of this book. 

We’d also like to thank Professor Richard A. Bucking¬ 
ham of the Abraham Lincoln School of Medicine, Univer¬ 
sity of Illinois for the provision of Fig. 8.114B. Finally, 
because we worked separately, distanced by, in some cases, 
thousands of miles, there are various people who gave local 
support, whom we would like to make mention of individu¬ 
ally. We’ve gratefully listed them here: 

Dr. Leonard Epp, Dr. Carl Morgan, Dr. Robert Shell- 
hamer, and Dr. Robert Cardell who profoundly influ¬ 
enced my career as a scientist and an educator. 

Richard L. Drake 

Dr. Sydney Friedman, Dr. Elio Raviola, and Dr. Charles 
Slonecker, for their inspiration and support and for 
instilling in me a passion for the discipline of Anatomy. 


Dr. Murray Morrison, Dr. Joanne Matsubara, Dr. Brian 
Westerberg, Laura Hall, and Jing Cui, for contributing 
images for the chapter on the head and neck. 

Dr. Bruce Crawford and Logan Lee, for help with images 
for the surface anatomy of the upper limb. 

Professor Elizabeth Akesson and Dr. Donna Ford, for 
their enthusiastic support and valuable critiques. 

Dr. Sam Wiseman, for contributing surgical and other 
images in the abdomen and head and neck chapters. 

A. Wayne Vogl 

Dr. Sahar Nasseri (senior specialist registrar) for help 
with the images and text and adding critical analysis 
on modern imaging. 

Drs. J. Healy, J. Lee, G. Rajeswarren, R. Pearce and 
B. Roberton for their support and constructive 
criticism. 

The radiology staff at Chelsea and Westminster Hospital 
and The Fortius Clinic. 

In particular, Mr. Andrew Williams, FRCS, whose 
relentless and unflagging support has been invaluable 
(and he mended my leg!). 

Adam W. M. Mitchell 


Dedications 


To my wife, Cheryl, who has supported me; and my parents, who have guided me. 

—Richard L. Drake 

To my family, to my professional colleagues and role models, and to my students—this book is for you. 
— A. Wayne Vogl 

To Cathy, Max, and Elsa 

—Adam W. M. Mitchell 


VII 


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Preface 


The 3rd edition of Gray’s Anatomy for Students builds on 
the past and looks toward the future. 

It maintains the goals and objectives of the 1st and 2nd 
editions while at the same time continuing to incorporate 
input from our readers and adjusting the content to align 
with the evolving educational environment. 

One of the major focuses of our attention as we pre¬ 
pared the 3rd edition was clinical content. The reason for 
this is that learning in context has become an important 
theme not only in medical education but in anatomical 
sciences education generally. We dealt with the clinical 
content in two ways. First, we reevaluated and updated 
the “In the clinic” boxes, clinical material in the body of 
the text, clinical cases at the end of the chapters and in the 
online resources, and in the surface anatomy section. 
Second, we added new clinical material so that the reader 
would have up-to-date examples relating anatomical infor¬ 
mation to clinical situations. 

In addition to updating and revising the clinical 
content, the section on cranial nerves has been signifi¬ 
cantly expanded. Understanding these important compo¬ 
nents of the nervous system is critical for students at 
every level. To facilitate student learning a new figure 


summarizing the location, function, and distribution of 
each cranial nerve has been added, as has a new figure 
summarizing how major structures, including cranial 
nerves, enter and leave the cranial cavity. We also have 
included a new figure illustrating the clinical importance 
of vascular structures in and around the cranial cavity. 

Another new feature in this edition relates to review 
materials. While these useful study aids have always been 
available on Student Consult as an online resource, in this 
edition the appropriate review materials for each chapter 
are listed at the beginning of that chapter. This information 
includes an online anatomy and embryology self-study 
course, medical clinical cases, physical therapy clinical 
cases, self-assessment questions, and more. 

We believe that with these changes the 3rd edition of 
Gray’s Anatomy for Students is a much improved version of 
the 2nd edition and hope that the book will continue to be 
a valuable learning resource for students. 

Richard L. Drake 
A. Wayne Vogl 
Adam W. M. Mitchell 
December 2013 


IX 


This page intentionally left blank 


About the Book 


The idea 

In the past 20 years or so, there have been many changes 
that have shaped how students learn human anatomy in 
medical and dental schools and in allied health programs, 
with curricula becoming either more integrated or more 
systems based. In addition, instructional methods focus on 
the use of small group activities with the goals of increas¬ 
ing the amount of self-directed learning, and acquiring the 
skills for the life-long acquisition of knowledge. An explo¬ 
sion of information in every discipline has also been a force 
in driving curricular change as it increases the amount to 
be learned without necessarily increasing the time avail¬ 
able. With these changes, we felt it was time for a new text 
to be written that would allow students to learn anatomy 
within the context of many different curricular designs, 
and within ever-increasing time constraints. 

We began in the fall of 2001 by considering the various 
approaches and formats that we might adopt, eventually 
deciding upon a regional approach to anatomy with each 
chapter having four sections. From the beginning, we 
wanted the book to be designed with multiple entry points, 
to be targeted at introductory level students in a broad 
spectrum of fields, and to be a student-oriented companion 
text for Gray's Anatomy, which is aimed at a more profes¬ 
sional audience. We wrote the text first and subsequently 
constructed all the artwork and illustrations to comple¬ 
ment and augment the words. Preliminary drafts of chap¬ 
ters, when complete, were distributed to an international 
editorial board of anatomists, educators, and anatomy stu¬ 
dents for review. Their comments were then considered 
carefully in the preparation of the final book. 

The text is not meant to be exhaustive in coverage, but 
to present enough anatomy to provide students with a 
structural and functional context in which to add further 
detail as they progress through their careers. Gray's 
Anatomy was used as the major reference, both for the text 
and for the illustrations, during the preparation of this 
book, and it is the recommended source for acquiring 
additional detail. 

The book 

Gray's Anatomy for Students is a clinically oriented, student- 
friendly textbook of human anatomy. It has been prepared 
primarily for students in a variety of professional programs 
(e.g., medical, dental, chiropractic, and physical therapy 


programs). It can be used by students in traditional, sys¬ 
temic, combined traditional/systemic, and problem-based 
curricula and will be particularly useful to students when 
lectures and laboratories in gross anatomy are minimal. 

ORGANIZATION 


Using a regional approach, Gray's Anatomy for Students 
progresses through the body in a logical fashion, building 
on the body’s complexities as the reader becomes more 
comfortable with the subject matter. Each chapter can be 
used as an independent learning module, and varying the 
sequence will not affect the quality of the educational 
experience. The sequence we have chosen to follow is back, 
thorax, abdomen, pelvis and perineum, lower limb, upper 
limb, and head and neck. 

We begin with “The body,” which contains an overview 
of the discipline of gross anatomy and an introduction to 
imaging modalities and general body systems. We follow 
this with the back because it is often the first area dissected 
by students. The thorax is next because of its central loca¬ 
tion and its contents (i.e., the heart, the great vessels, and 
the lungs). This also begins a progression through the 
body’s cavities. The abdomen and pelvis and perineum 
follow logically in sequence from the thorax. Continuing 
downward toward the feet, the lower limb is next, followed 
by the upper limb. The last region discussed is the head and 
neck. This region contains some of the most difficult 
anatomy in the body. Covering all other regions first gives 
the student the opportunity to build a strong foundation 
from which to understand this complex region. 

CONTENT 

Each regional anatomy chapter consists of four consecu¬ 
tive sections: conceptual overview, regional anatomy, 
surface anatomy, and clinical cases. 

The conceptual overview provides the basis on which 
information in the later sections is built. This section can 
be read independently of the rest of the text by students 
who require only a basic level of understanding and can 
also be read as a summary of important concepts after the 
regional anatomy has been mastered. 

The regional anatomy section provides more detailed 
anatomy along with a substantial amount of relevant clin¬ 
ical correlations. It is not an exhaustive discussion but 
instead provides information to a level that we feel is neces¬ 
sary for understanding the organization of the region, xi 




About the Book 


Throughout this section, two levels of clinical material are 
provided. Clinical hooks are fully integrated with the main 
anatomical text and function to relate (“hook”) the 
anatomy discussed directly to a clinical application without 
taking students out of their train of thought and without 
disrupting the flow of the text. Although fully integrated 
with the anatomical text, these passages are differentiated 
from it by the use of green highlighting. “In the clinic” 
summaries provide students with useful and relevant clini¬ 
cal information demonstrating how applying anatomical 
knowledge facilitates the solving of clinical problems. 
These are spread throughout the text close to the most 
relevant anatomical discussion. 

Surface anatomy assists students in visualizing the rela¬ 
tionship between anatomical structures and surface land¬ 
marks. This section also provides students with practical 
applications of the anatomical information, combining 
visual inspection with functional assessment, as occurs 
during any type of patient examination. 

The final section of each chapter consists of clinical 
cases. These cases represent the third level of clinical 
material in the book. In these cases the clinical problem 
is described, and a step-by-step process of questions and 
answers leads the reader to the resolution of the case. The 
inclusion of these cases in each chapter provides students 
with the opportunity to apply an understanding of 
anatomy to the resolution of a clinical problem. 

Illustrations are an integral part of any anatomy 
text. They must present the reader with a visual image 
that brings the text to life and presents views that will 
assist in the understanding and comprehension of the 
anatomy. The artwork in this text accomplishes all of 
these goals. The illustrations are original and vibrant, 
and many views are unique. They have been designed 
to integrate with the text, present the anatomy in new 
ways, deal with the issues that students find particularly 
difficult, and provide a conceptual framework for building 
further understanding. To ensure that the illustrations of 
the book work together and to enable students to cross- 
ref er from one illustration to another, we have used stan¬ 
dard colors throughout the book, except where indicated 
otherwise. 



artery 



lymphatic 


sympathetic fiber 


parasympathetic fiber 



preganglionic fiber (solid) 


postganglionic fiber (dotted) 


The position and size of the artwork was one of the 
parameters considered in the overall design of each page 
of the book. 

Clinical images are also an important tool in under¬ 
standing anatomy and are abundant throughout the text. 
Examples of state-of-the-art medical imaging, including 
MRIs, CTs, PETs, and ultrasound, as well as high-quality 
radiographs, provide students with additional tools to 
increase their ability to visualize anatomy in vivo and, 
thus, increase their understanding. 


What the book does not contain 

Gray’s Anatomy for Students focuses on gross anatomy. 
While many curricula around the world are being pre¬ 
sented in a more integrated format combining anatomy, 
physiology, histology, and embryology, we have focused this 
textbook on understanding only the anatomy and its appli¬ 
cation to clinical problems. Except for some brief references 
to embryology where necessary for a better understanding 
of the anatomy, material from other disciplines is not 
included. We felt that there are many outstanding text¬ 
books covering these subject areas, and that trying to 
cover everything in a single book would produce a text of 
questionable quality and usefulness, not to mention enor¬ 
mous size! 


xii 


l^j j vein 
() nerve 


Terminology 

In any anatomical text or atlas, terminology is always 
an interesting issue. In 1989, the Federative Committee 
on Anatomical Terminology (FCAT) was formed and 






















About the Book 


was charged with developing the official terminology of 
the anatomical sciences. The Terminologia Anatomica 
(2nd edition, Thieme, Stuttgart/New York, 2011) was a 
joint publication by this group and the 56 member associa¬ 
tions of the International Federation of Associations of 
Anatomists (IFAA). We have chosen to use the terminology 
presented in this publication in the interest of uniformity. 
Other terminology is not incorrect; we just felt that using 
terminology from this single, internationally recognized 
source would be the most logical and straightforward 
approach. 

Although we use anatomical terms for orientation as 
much as possible, we also use terms such as “behind” or 
“in front of” occasionally to make the text more readable. 
In these cases, the context clarifies the meaning. 

Anatomical use of adverbs 

During the writing of this book, we had many long discus¬ 
sions about how we were going to describe anatomical rela¬ 
tionships as clearly as possible, but maintain the readability 
of the text. One issue that arose continually in our discus¬ 
sions was the correct use of the “-ly” adverb form of 


anatomical orientation terms, such as anterior, posterior, 
superior, inferior, lateral, and medial. We reached the fol¬ 
lowing consensus: 

-ly adverbs e.g., anteriorly, posteriorly, have been used to 
modify (describe) verbs in passages where an action or 
direction is mentioned. For example, “The trachea 
passes inferiorly through the thorax.” 
circumstantial adverbs, e.g., anterior, posterior, have been 
used to indicate the fixed location of an anatomical 
feature. For example, “The trachea is anterior to the 
esophagus.” 

Furthermore, both usages may occur in the same 
passage. For example, “The trachea passes inferiorly 
through the thorax, anterior to the esophagus.” 

We have very much enjoyed the process of putting this 
book together. We hope that you enjoy using it to the same 
degree. 

Richard L. Drake 
A. Wayne Vogl 
Adam W. M. Mitchell 


xiii 


This page intentionally left blank 


Index of Clinical Content 


1 The body 

In the Clinic 

Determination of skeletal age 14 

Bone marrow transplants 15 

Bone fractures 16 

Avascular necrosis 16 

Osteoporosis 17 

Epiphyseal fractures 18 

Degenerative joint disease 22 

Joint replacement 24 

The importance of fascias 25 

Muscle paralysis 26 

Muscle atrophy 26 

Muscle injuries and strains 26 

Atherosclerosis 27 

Varicose veins 28 

Anastomoses and collateral circulation 28 
Lymph nodes 31 
Dermatomes and myotomes 37 
Referred pain 48 

Clinical Case 

Appendicitis 50 


2 Back 


In the Clinic 

Spina bifida 74 
Vertebroplasty 74 
Scoliosis 75 
Kyphosis 76 

Variation in vertebral numbers 76 
The vertebrae and cancer 77 
Osteoporosis 77 
Back pain 79 

Herniation of intervertebral discs 79 

Joint diseases 80 

Ligamenta flava 82 

Vertebral fractures 82 

Surgical procedures on the back 84 

Nerve injuries affecting superficial back muscles 99 

Lumbar cerebrospinal fluid tap 106 


Herpes zoster 109 

Back pain—alternative explanations 110 

Clinical Cases 

Sciatica versus lumbago 118 
Cervical spinal cord injury 118 
Psoas abscess 119 
Dissecting thoracic aneurysm 119 
Sacral tumor 120 


3 Thorax 


In the Clinic 

Axillary tail of breast 141 
Breast cancer 141 
Cervical ribs 150 

Collection of sternal bone marrow 152 

Rib fractures 152 

Surgical access to the chest 160 

Thoracostomy (chest) tube insertion 160 

Intercostal nerve block 160 

Pleural effusion 167 

Pneumothorax 167 

Imaging the lungs 178 

High-resolution lung CT 178 

Bronchoscopy 178 

Lung cancer 179 

Pericarditis 184 

Pericardial effusion 184 

Constrictive pericarditis 184 

Valve disease 197 

Clinical terminology for coronary arteries 201 
Heart attack 202 

Classic symptoms of heart attack 203 
Are heart attack symptoms the same in men and 
women? 203 

Common congenital heart defects 203 
Cardiac auscultation 204 
Cardiac conduction system 206 
Ectopic parathyroid glands in the thymus 212 
Venous access for central and dialysis lines 215 
Using the superior vena cava to access the inferior 
vena cava 215 
Coarctation of the aorta 217 





Index of Clinical Content 


xvi 


Thoracic aorta 217 
Aortic arch and its anomalies 217 
Abnormal origin of great vessels 217 
The vagus nerves, recurrent laryngeal nerves, and 
hoarseness 221 
Esophageal cancer 224 
Esophageal rupture 225 

Clinical Cases 

Cervical rib 241 
Lung cancer 242 
Chest wound 242 
Myocardial infarction 243 
Broken pacemaker 246 
Coarctation of the aorta 247 
Aortic dissection 247 
Pneumonia 249 
Esophageal cancer 250 
Venous access 251 


4 Abdomen 

In the Clinic 

Surgical incisions 278 
Laparoscopic surgery 279 
Cremasteric reflex 299 
Masses around the groin 301 
Peritoneum 305 
The greater omentum 308 
Epithelial transition between the abdominal 
esophagus and stomach 315 
Duodenal ulceration 315 

Examination of the upper gastrointestinal tract 316 
Examination of the bowel lumen 316 
Examination of the bowel wall and extrinsic 
masses 316 

Meckel's diverticulum 318 
Computed tomography (CT) scanning and magnetic 
resonance imaging (MRI) 318 
Carcinoma of the stomach 318 
Appendicitis 322 

Congenital disorders of the gastrointestinal 
tract 325 

Bowel obstruction 326 
Diverticular disease 327 
Ostomies 327 
Annular pancreas 336 


Pancreatic cancer 336 

Segmental anatomy of the liver 339 

Gallstones 341 

Jaundice 341 

Spleen disorders 342 

Vascular supply to the gastrointestinal system 351 

Hepatic cirrhosis 356 

Surgery for obesity 365 

Psoas muscle abscess 371 

Diaphragmatic hernias 372 

Hiatus hernia 373 

Urinary tract stones 380 

Urinary tract cancer 381 

Nephrostomy 382 

Kidney transplant 383 

Investigation of the urinary tract 385 

Abdominal aortic stent graft 389 

Inferior vena cava filter 391 

Retroperitoneal lymph node surgery 393 

Clinical Cases 

Traumatic rupture of the diaphragm 410 
Chronic thrombosis of the inferior vena cava 410 
Liver biopsy in patients with suspected liver 
cirrhosis 411 
Hodgkin's lymphoma 412 
Inguinal hernia 413 
Ureteric stone 413 
Intraabdominal abscess 414 
Complications of an abdominoperineal 
resection 415 

Carcinoma of the head of the pancreas 417 
Caval obstruction 418 
Diverticular disease 418 
Endoleak after endovascular repair of abdominal 
aortic aneurysm 419 
Metastatic lesions in the liver 420 


5 Pelvis and perineum 

In the Clinic 

Bone marrow biopsy 444 
Pelvic fracture 446 

Common problems with the sacro-iliac joints 448 
Pelvic measurements in obstetrics 454 
Defecation 456 
Episiotomy 460 




Index of Clinical Content 


Digital rectal examination 462 

Carcinoma of the colon and rectum 462 

Bladder stones 465 

Suprapubic catheterization 466 

Bladder cancer 466 

Bladder infection 469 

Urethral catheterization 469 

Testicular tumors 470 

Vasectomy 472 

Prostate problems 474 

Ovarian cancer 477 

Imaging the ovary 477 

Hysterectomy 478 

Tubal ligation 479 

Carcinoma of the cervix and uterus 480 
The recto-uterine pouch 481 
Pudendal block 491 
Prostatectomy and impotence 495 
Abscesses in the ischio-anal fossae 504 
Hemorrhoids 504 
Urethral rupture 512 

Clinical Cases 

Varicocele 527 

Sciatic nerve compression 528 

Pelvic kidney 528 

Left common iliac artery obstruction 529 
Iatrogenic ureteric injury 530 
Ectopic pregnancy 530 
Uterine tumor 531 
Uterine fibroids 532 


6 Lower limb 


In the Clinic 

Pelvic fractures 553 
Femoral neck fractures 557 
Intertrochanteric fractures 558 
Femoral shaft fractures 558 
Varicose veins 569 
Deep vein thrombosis 569 
Vascular access to the lower limb 573 
Trendelenburg's sign 577 
Intramuscular injections 581 
Compartment syndrome 590 
Muscle injuries to the lower limb 599 
Peripheral vascular disease 603 


Soft tissue injuries to the knee 613 

Degenerative joint disease/osteoarthritis 614 

Examination of the knee joint 614 

Anterolateral ligament of the knee 615 

Achilles tendon rupture 623 

Neurological examination of the legs 625 

Footdrop 633 

Fracture of the talus 638 

Ankle fractures 641 

Bunions 645 

Morton's neuroma 661 

Clinical Cases 

Varicose veins 672 
Knee joint injury 673 
Fracture of neck of femur 676 
Deep vein thrombosis 677 
Ruptured calcaneal tendon 678 
Popliteal artery aneurysm 679 
Anterior talofibular ligament tear 680 


7 Upper limb 

In the Clinic 

Fracture of the proximal humerus 705 
Fractures of the clavicle and dislocations of the 
acromioclavicular and sternoclavicular joints 711 
Dislocations of the glenohumeral joint 712 
Rotator cuff disorders 712 
Inflammation of the subacromial (subdeltoid) 
bursa 713 

Quadrangular space syndrome 720 

"Winging" of the scapula 727 

Imaging the blood supply to the upper limb 737 

Trauma to the arteries of the upper limb 737 

Subclavian/axillary venous access 737 

Injuries to the brachial plexus 747 

Breast cancer 749 

Rupture of biceps tendon 755 

Blood pressure measurement 756 

Radial nerve injury in the arm 763 

Median nerve injury in the arm 763 

Supracondylar fracture of the humerus 766 

Pulled elbow 766 

Developmental changes in the elbow joint 767 
Fracture of the head of radius 768 





Index of Clinical Content 


'Tennis" and "golfer's" elbow (epicondylitis) 768 
Elbow arthritis 768 
Ulnar nerve injury at the elbow 768 
Construction of a dialysis fistula 770 
Fractures of the radius and ulna 774 
Transection of the radial or ulnar artery 783 
Fracture of the scaphoid and avascular necrosis of 
the proximal scaphoid 797 
Carpal tunnel syndrome 798 
Snuffbox 801 

De Quervain's syndrome 802 
Tenosynovitis 802 
Trigger finger 802 
Allen's test 814 
Venipuncture 814 
Ulnar nerve injury 816 
Radial nerve injury 818 

Clinical Cases 

Shoulder problem after falling on an outstretched 
hand 829 
Winged scapula 829 
Brachial plexus nerve block 830 
Complication of a fractured first rib 830 
Median nerve compression 831 
Immobilizing the extensor digitorum muscle 831 
Torn supraspinatus tendon 832 
How to examine the hand 833 
Shoulder joint problem 834 


8 Head and neck 


In the Clinic 

Medical imaging of the head 871 
Fractures of the skull vault 872 
Hydrocephalus 877 
Cerebrospinal fluid leak 878 
Meningitis 878 
Brain tumors 878 
Stroke 883 
Endarterectomy 885 
Intracerebral aneurysms 885 
Scalp and meninges 890 
Head injury 891 

Types of intracranial hemorrhage 891 


Emissary veins 893 
Concussion 893 

Clinical assessment of patients with head injury 893 

Treatment of head injury 893 

Cranial nerve lesions 901 

Overview of cranial nerves 901 

Parotid gland 913 

Facial nerve [VII] palsy (Bell's palsy) 921 
Trigeminal neuralgia 921 
Scalp laceration 926 
Orbital fracture 928 
Horner's syndrome 931 
Examination of the eye 940 
Glaucoma 948 
Cataracts 948 
Ophthalmoscopy 949 

High-definition optical coherence tomography 951 
Examination of the ear 957 
Swimmer's ear 957 
Surfer's ear 958 

Tympanic membrane perforation 958 
Mastoiditis 961 
Lingual nerve injury 987 
Dental anesthesia 989 
Fascial planes of the head and neck 1004 
Central venous access 1005 
Jugular venous pulse 1013 
Thyroid gland 1020 
Thyroidectomy 1021 
Thyroid gland pathology 1021 
Ectopic parathyroid glands 1022 
Recurrent laryngeal nerve palsy 1034 
Clinical lymphatic drainage of the head and 
neck 1040 
Tracheostomy 1065 
Laryngoscopy 1065 
Deviated nasal septum 1077 

Clinical Cases 

Multinodular goiter 1129 

Parotid duct calculus 1130 

Extradural hematoma 1131 

Stenosis of the internal carotid artery 1132 

Posterior communicating artery aneurysm 1133 

Recurrent epistaxis 1133 

Complication of orbital fracture 1134 

Pituitary macroadenoma 1135 




Contents 



The body 


What is anatomy? 2 

How can gross anatomy be studied? 2 
Important anatomical terms 2 

Imaging 5 

Diagnostic imaging techniques 5 
Nuclear medicine imaging 8 

Image interpretation 10 

Plain radiography 10 
Computed tomography 10 
Magnetic resonance imaging 11 
Nuclear medicine imaging 11 

Safety in imaging 11 

Body systems 12 

Skeletal system 12 

Cartilage 12 
Bone 13 
Joints 18 

Skin and fascias 24 
Skin 24 
Fascia 24 

Muscular system 25 
Cardiovascular system 27 
Lymphatic system 29 

Lymphatic vessels 29 
Lymph nodes 30 
Lymphatic trunks and ducts 30 
Nervous system 31 

Central nervous system 31 
Functional subdivisions of the CNS 32 

Somatic part of the nervous system 33 
Visceral part of the nervous system 38 

Other systems 48 

Clinical case 50 



Back 


Conceptual overview 53 

General description 53 
Functions 54 
Support 54 
Movement 54 

Protection of the nervous system 55 


Component parts 56 
Bones 56 
Muscles 57 
Vertebral canal 59 
Spinal nerves 60 
Relationship to other regions 61 
Head 61 

Thorax, abdomen, and pelvis 62 
Limbs 62 
Key features 62 

Long vertebral column and short spinal cord 62 
Intervertebral foramina and spinal nerves 63 
Innervation of the back 63 

Regional anatomy 64 

Skeletal framework 64 

Vertebrae 64 

Intervertebral foramina 72 

Posterior spaces between vertebral arches 73 

Joints 77 

Joints between vertebrae in the back 77 
Ligaments 80 

Anterior and posterior longitudinal ligaments 80 
Ligamenta flava 80 

Supraspinous ligament and ligamentum nuchae 81 
Interspinous ligaments 82 
Back musculature 84 
Superficial group of back muscles 84 
Intermediate group of back muscles 90 
Deep group of back muscles 92 
Suboccipital muscles 97 
Spinal cord 99 
Vasculature 100 
Meninges 103 

Arrangement of structures in the vertebral 
canal 104 
Spinal nerves 106 

Surface anatomy 111 

Back surface anatomy 111 
Absence of lateral curvatures 111 
Primary and secondary curvatures in the sagittal 
plane 112 

Useful non vertebral skeletal landmarks 112 
How to identify specific vertebral spinous 
processes 114 

Visualizing the inferior ends of the spinal cord and 
subarachnoid space 115 
Identifying major muscles 116 

Clinical cases 118 


xix 








Contents 



Thorax 


Conceptual overview 123 

General description 123 
Functions 124 
Breathing 124 
Protection of vital organs 124 
Conduit 124 
Component parts 124 
Thoracic wall 124 
Superior thoracic aperture 126 
Inferior thoracic aperture 126 
Diaphragm 127 
Mediastinum 128 
Pleural cavities 128 
Relationship to other regions 130 
Neck 130 
Upper limb 130 
Abdomen 130 
Breast 131 
Key features 132 
Vertebral level TIV/V 132 
Venous shunts from left to right 132 
Segmental neurovascular supply of thoracic 
wall 134 

Sympathetic system 136 

Flexible wall and inferior thoracic aperture 136 

Innervation of the diaphragm 138 

Regional anatomy 139 

Pectoral region 139 

Breast 139 

Muscles of the pectoral region 142 
Thoracic wall 143 
Skeletal framework 143 
Intercostal spaces 150 
Diaphragm 161 
Arterial supply 162 
Venous drainage 162 
Innervation 162 

Movements of the thoracic wall and diaphragm 
during breathing 162 
Pleural cavities 162 
Pleura 163 
Lungs 167 
Mediastinum 180 
Middle mediastinum 180 
Superior mediastinum 210 
Posterior mediastinum 222 
Anterior mediastinum 230 

Surface anatomy 231 

Thorax surface anatomy 231 


How to count ribs 231 
Surface anatomy of the breast in women 232 
Visualizing structures at the TIV/V vertebral 
level 232 

Visualizing structures in the superior 
mediastinum 234 

Visualizing the margins of the heart 235 
Where to listen for heart sounds 236 
Visualizing the pleural cavities and lungs; pleural 
recesses; and lung lobes and fissures 236 
Where to listen for lung sounds 238 

Clinical cases 241 


□ 


Abdomen 


Conceptual overview 255 

General description 255 
Functions 256 

Houses and protects major viscera 256 
Breathing 258 

Changes in intraabdominal pressure 258 
Component parts 259 
Wall 259 

Abdominal cavity 260 
Inferior thoracic aperture 262 
Diaphragm 262 
Pelvic inlet 263 

Relationship to other regions 263 
Thorax 263 
Pelvis 263 
Lower limb 264 
Key features 265 

Arrangement of abdominal viscera in the adult 265 
Skin and muscles of the anterior and lateral 
abdominal wall and thoracic intercostal 
nerves 268 

The groin is a weak area in the anterior abdominal 
wall 269 

Vertebral level LI 271 

The gastrointestinal system and its derivatives are 
supplied by three major arteries 271 
Venous shunts from left to right 273 
All venous drainage from the gastrointestinal system 
passes through the liver 274 
Abdominal viscera are supplied by a large 
prevertebral plexus 276 

Regional anatomy 277 

Surface topography 277 
Four-quadrant pattern 277 
Nine-region pattern 278 


XX 







Contents 


Abdominal wall 280 

Superficial fascia 280 
Anterolateral muscles 282 
Extraperitoneal fascia 288 
Peritoneum 288 
Innervation 289 

Arterial supply and venous drainage 291 
Lymphatic drainage 292 
Groin 292 
Inguinal canal 294 
Inguinal hernias 299 
Abdominal viscera 303 
Peritoneum 303 
Peritoneal cavity 304 
Organs 310 
Arterial supply 343 
Venous drainage 354 
Lymphatics 358 
Innervation 358 

Posterior abdominal region 366 

Posterior abdominal wall 367 
Viscera 373 
Vasculature 387 
Lymphatic system 392 
Nervous system in the posterior abdominal 
region 394 

Sympathetic trunks and splanchnic nerves 394 

Surface anatomy 402 

Abdomen surface anatomy 402 
Defining the surface projection of the abdomen 402 
How to find the superficial inguinal ring 403 
How to determine lumbar vertebral levels 404 
Visualizing structures at the LI vertebral level 405 
Visualizing the position of major blood vessels 406 
Using abdominal quadrants to locate major 
viscera 407 

Defining surface regions to which pain from the gut is 
referred 408 

Where to find the kidneys 409 
Where to find the spleen 409 

Clinical cases 410 



Pelvis and perineum 


Conceptual overview 423 

General description 423 
Functions 423 

Contain and support bladder, rectum, anal canal, and 
reproductive tracts 423 
Anchors the roots of the external genitalia 425 


Component parts 426 
Pelvic inlet 426 
Pelvic walls 426 
Pelvic outlet 428 
Pelvic floor 429 
Pelvic cavity 429 
Perineum 430 

Relationship to other regions 432 
Abdomen 432 
Lower limb 433 
Key features 434 

The pelvic cavity projects posteriorly 434 
Important structures cross the ureters in the pelvic 
cavity 435 

The prostate in men and the uterus in women are 
anterior to the rectum 436 
The perineum is innervated by sacral spinal cord 
segments 436 

Nerves are related to bone 437 
Parasympathetic innervation from spinal cord levels 
S2 to S4 controls erection 438 
Muscles and fascia of the pelvic floor and perineum 
intersect at the perineal body 439 
The course of the urethra is different in men and 
women 440 

Regional anatomy 441 

Pelvis 441 

Bones 441 
Joints 446 
Orientation 448 

Differences between men and women 448 
True pelvis 449 
Viscera 460 
Fascia 481 
Peritoneum 481 
Nerves 486 
Blood vessels 495 
Lymphatics 501 
Perineum 502 
Borders and ceiling 502 

Ischio-anal fossae and their anterior recesses 504 

Anal triangle 504 

Urogenital triangle 506 

Somatic nerves 513 

Visceral nerves 515 

Bloodvessels 516 

Veins 516 

Lymphatics 519 

Surface anatomy 520 

Surface anatomy of the pelvis and perineum 520 
Orientation of the pelvis and perineum in the 
anatomical position 520 





Contents 


xxii 


How to define the margins of the perineum 520 
Identification of structures in the anal triangle 522 
Identification of structures in the urogenital triangle 
of women 523 

Identification of structures in the urogenital triangle 
of men 524 

Clinical cases 527 



Lower limb 


Conceptual overview 535 

General introduction 535 
Function 537 

Support the body weight 537 
Locomotion 537 
Component parts 539 
Bones and joints 539 
Muscles 543 

Relationship to other regions 545 
Abdomen 545 
Pelvis 545 
Perineum 545 
Key points 545 

Innervation is by lumbar and sacral spinal 
nerves 545 

Nerves related to bone 550 
Superficial veins 550 

Regional anatomy 551 

Bony pelvis 551 
Proximal femur 554 
Hip joint 558 

Gateways to the lower limb 562 

Nerves 563 

Arteries 566 

Veins 568 

Lymphatics 570 

Deep fascia and the saphenous opening 571 
Femoral triangle 572 
Gluteal region 574 
Muscles 574 
Nerves 579 
Arteries 582 
Veins 583 
Lymphatics 583 
Thigh 583 
Bones 584 
Muscles 589 
Arteries 600 
Veins 603 


Nerves 603 
Knee joint 606 
Tibiofibular joint 616 
Popliteal fossa 616 
Leg 618 
Bones 618 
Joints 620 

Posterior compartment of leg 621 
Lateral compartment of leg 628 
Anterior compartment of leg 630 
Foot 633 
Bones 634 
Joints 638 

Tarsal tunnel, retinacula, and arrangement of major 
structures at the ankle 646 
Arches of the foot 648 
Plantar aponeurosis 649 
Fibrous sheaths of toes 649 
Extensor hoods 650 
Intrinsic muscles 650 
Arteries 657 
Veins 659 
Nerves 659 

Surface anatomy 663 

Lower limb surface anatomy 663 
Avoiding the sciatic nerve 663 
Finding the femoral artery in the femoral 
triangle 664 

Identifying structures around the knee 664 
Visualizing the contents of the popliteal fossa 666 
Finding the tarsal tunnel—the gateway to the 
foot 667 

Identifying tendons around the ankle and in the 
foot 668 

Finding the dorsalis pedis artery 669 
Approximating the position of the plantar arterial 
arch 669 

Major superficial veins 670 
Pulse points 671 

Clinical cases 672 


Upper limb 


Conceptual overview 685 

General description 685 
Functions 686 
Positioning the hand 686 
The hand as a mechanical tool 689 
The hand as a sensory tool 689 






Contents 


Component parts 690 

Bones and joints 690 
Muscles 692 

Relationship to other regions 693 

Neck 693 

Back and thoracic wall 694 
Keypoints 695 

Innervation by cervical and upper thoracic 
nerves 695 

Nerves related to bone 699 
Superficial veins 700 
Orientation of the thumb 701 

Regional anatomy 702 

Shoulder 702 

Bones 702 
Joints 705 
Muscles 713 

Posterior scapular region 7 7 6 

Muscles 717 

Gateways to the posterior scapular region 717 
Nerves 719 
Arteries and veins 719 
Axilla 721 

Axillary inlet 723 

Anterior wall 723 

Medial wall 726 

Lateral wall 727 

Posterior wall 728 

Gateways in the posterior wall 730 

Floor 731 

Contents of the axilla 731 
Arm 750 
Bones 751 
Muscles 754 
Arteries and veins 756 
Nerves 760 
Elbow joint 764 
Cubital fossa 768 
Forearm 771 
Bones 773 
Joints 774 

Anterior compartment of the forearm 776 

Muscles 776 
Arteries and veins 782 
Nerves 784 

Posterior compartment of the forearm 785 

Muscles 785 
Arteries and veins 791 
Nerves 792 
Hand 792 
Bones 793 
Joints 795 


Carpal tunnel and structures at the wrist 798 

Palmar aponeurosis 800 

Palmaris brevis 800 

Anatomical snuffbox 800 

Fibrous digital sheaths 801 

Extensor hoods 802 

Muscles 804 

Arteries and veins 810 

Nerves 814 

Surface anatomy 819 

Upper limb surface anatomy 819 
Bony landmarks and muscles of the posterior 
scapular region 819 

Visualizing the axilla and locating contents and 
related structures 820 
Locating the brachial artery in the arm 821 
The triceps brachii tendon and position of the radial 
nerve 822 

Cubital fossa (anterior view) 822 
Identifying tendons and locating major vessels and 
nerves in the distal forearm 824 
Normal appearance of the hand 825 
Position of the flexor retinaculum and the recurrent 
branch of the median nerve 826 
Motor function of the median and ulnar nerves in the 
hand 826 

Visualizing the positions of the superficial and deep 
palmar arches 827 
Pulse points 827 

Clinical cases 829 



Head and neck 


Conceptual overview 837 

General description 837 
Head 837 
Neck 839 
Functions 841 
Protection 841 

Contains upper parts of respiratory and digestive 
tracts 841 
Communication 841 
Positioning the head 841 
Connects the upper and lower respiratory and 
digestive tracts 841 
Component parts 842 
Skull 842 

Cervical vertebrae 844 


xxiii 




Contents 


Hyoid bone 845 
Soft palate 846 
Muscles 846 

Relationship to other regions 847 

Thorax 847 
Upper limbs 847 
Key features 848 
Vertebral levels CIII/IV and CV/VI 848 
Airway in the neck 849 
Cranial nerves 850 
Cervical nerves 851 

Functional separation of the digestive and respiratory 
passages 851 
Triangles of the neck 854 
Regional anatomy 855 
Skull 855 
Anterior view 855 
Lateral view 857 
Posterior view 859 
Superior view 860 
Inferior view 860 
Cranial cavity 864 
Roof 864 
Floor 865 
Meninges 873 
Cranial dura mater 873 
Arachnoid mater 876 
Pia mater 877 

Arrangement of meninges and spaces 877 
Brain and its blood supply 879 
Brain 879 
Blood supply 879 
Venous drainage 886 
Cranial nerves 894 
Olfactory nerve [I] 896 

Optic nerve [II] 896 
Oculomotor nerve [III] 897 
Trochlear nerve [IV] 897 
Trigeminal nerve [V] 898 

Ophthalmic nerve [Vd 898 
Maxillary nerve [V 2 ] 898 

Mandibular nerve [V 3 ] 898 

Abducent nerve [VI] 898 
Facial nerve [VII] 898 
Vestibulocochlear nerve [VIII] 899 
Glossopharyngeal nerve [IX] 899 
Vagus nerve [X] 900 
Accessory nerve [XI] 900 
Hypoglossal nerve [XII] 900 
Face 904 
Muscles 904 
Parotid gland 911 
Innervation 914 


Vessels 916 
Scalp 922 
Layers 922 
Innervation 924 
Vessels 925 
Lymphatic drainage 926 
Orbit 927 
Bony orbit 927 
Eyelids 928 
Lacrimal apparatus 932 
Sensory innervation 933 
Fissures and foramina 934 
Fascial specializations 935 
Muscles 936 
Vessels 941 
Innervation 942 
Eyeball 947 
Ear 953 

External ear 954 
Middle ear 958 
Internal ear 965 

Temporal and infratemporal fossae 972 

Bony framework 973 
Temporomandibular joints 975 
Masseter muscle 977 
Temporal fossa 978 
Infratemporal fossa 981 
Pterygopalatine fossa 992 
Skeletal framework 993 
Gateways 994 
Contents 994 
Neck 1000 
Fascia 1000 

Superficial venous drainage 1003 
Anterior triangle of the neck 1006 
Posterior triangle of the neck 1023 
Root of the neck 1030 
Pharynx W40 
Skeletal framework 1041 
Pharyngeal wall 1042 
Fascia 1045 

Gaps in the pharyngeal wall and structures passing 
through them 1046 
Nasopharynx 1046 
Oropharynx 1048 
Laryngopharynx 1048 
Tonsils 1048 
Vessels 1049 
Nerves 1051 
Larynx 1052 
Laryngeal cartilages 1053 
Extrinsic ligaments 1056 
Intrinsic ligaments 1057 


Contents 


Laryngeal joints 1058 
Cavity of the larynx 1059 
Intrinsic muscles 1061 
Function of the larynx 1064 
Vessels 1066 
Nerves 1068 
Nasal cavities 106 9 
Lateral wall 1070 
Regions 1071 

Innervation and blood supply 1072 
Skeletal framework 1072 
External nose 1074 
Paranasal sinuses 1074 
Walls, floor, and roof 1076 
Nares 1080 
Choanae 1081 
Gateways 1082 
Vessels 1082 
Innervation 1085 
Oral cavity 1 087 

Multiple nerves innervate the oral cavity 1088 

Skeletal framework 1088 

Walls: the cheeks 1091 

Floor 1092 

Tongue 1095 

Salivary glands 1102 


Roof—palate 1105 
Oral fissure and lips 1113 
Oropharyngeal isthmus 1114 
Teeth and gingivae 1114 

Surface anatomy 1120 

Head and neck surface anatomy 1120 

Anatomical position of the head and major 
landmarks 1120 

Visualizing structures at the CIII/CIV and CVI vertebral 
levels 1121 

How to outline the anterior and posterior triangles of 
the neck 1122 

How to locate the cricothyroid ligament 1123 

How to find the thyroid gland 1124 

Estimating the position of the middle meningeal 
artery 1124 

Major features of the face 1125 

The eye and lacrimal apparatus 1126 

External ear 1127 

Pulse points 1128 

Clinical cases 1129 


XXV 


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ADDITIONAL LEARNING RESOURCES 
for Chapter 1, The Body, 
on STUDENT CONSULT 

( ) 


Image Library—illustrations for Chapter 1 
Short Questions—these are questions requiring 
short responses, Chapter 1 





The Body 

What is anatomy? 

How can gross anatomy be studied? 

Important anatomical terms 

Imaging 

Diagnostic imaging techniques 
Nuclear medicine imaging 
Image interpretation 
Plain radiography 
Computed tomography 
Magnetic resonance imaging 
Nuclear medicine imaging 
Safety in imaging 

Body systems 

Skeletal system 
Cartilage 
Bone 
Joints 

Skin and fascias 
Skin 
Fascia 

Muscular system 
Cardiovascular system 
Lymphatic system 

Lymphatic vessels 
Lymph nodes 

Lymphatic trunks and ducts 
Nervous system 

Central nervous system 
Functional subdivisions of the CNS 
Somatic part of the nervous system 
Visceral part of the nervous system 
Other systems 


Clinical cases 



The Body 


What is anatomy? 

Anatomy includes those structures that can be seen grossly 
(without the aid of magnification) and microscopically 
(with the aid of magnification). Typically when used by 
itself, the term anatomy tends to mean gross or macro¬ 
scopic anatomy—that is, the study of structures that can 
be seen without using a microscopic. Microscopic anatomy, 
also called histology, is the study of cells and tissues using 
a microscope. 

Anatomy forms the basis for the practice of medicine. 
Anatomy leads the physician toward an understanding of 
a patient’s disease, whether he or she is carrying out a 
physical examination or using the most advanced imaging 
techniques. Anatomy is also important for dentists, chiro¬ 
practors, physical therapists, and all others involved in any 
aspect of patient treatment that begins with an analysis of 
clinical signs. The ability to interpret a clinical observation 
correctly is therefore the endpoint of a sound anatomical 
understanding. 

Observation and visualization are the primary tech¬ 
niques a student should use to learn anatomy. Anatomy is 
much more than just memorization of lists of names. 
Although the language of anatomy is important, the 
network of information needed to visualize the position of 
physical structures in a patient goes far beyond simple 
memorization. Knowing the names of the various branches 
of the external carotid artery is not the same as being able 
to visualize the course of the lingual artery from its origin 
in the neck to its termination in the tongue. Similarly, 
understanding the organization of the soft palate, how it is 
related to the oral and nasal cavities, and how it moves 
during swallowing is very different from being able to recite 
the names of its individual muscles and nerves. An under¬ 
standing of anatomy requires an understanding of the 
context in which the terminology can be remembered. 

How can gross anatomy be studied? 

The term anatomy is derived from the Greek word temnein, 
meaning “to cut.” Clearly, therefore, the study of anatomy 
is linked, at its root, to dissection, although dissection of 
cadavers by students is now augmented, or even in some 
cases replaced, by viewing prosected (previously dissected) 
material and plastic models, or using computer teaching 
modules and other learning aids. 

Anatomy can be studied following either a regional or a 
systemic approach. 

■ With a regional approach, each region of the body 

is studied separately and all aspects of that region 


are studied at the same time. For example, if the thorax 
is to be studied, all of its structures are examined. 
This includes the vasculature, the nerves, the bones, 
the muscles, and all other structures and organs 
located in the region of the body defined as the 
thorax. After studying this region, the other regions of 
the body (i.e., the abdomen, pelvis, lower limb, upper 
limb, back, head, and neck) are studied in a similar 
fashion. 

■ In contrast, in a systemic approach, each system of 
the body is studied and followed throughout the entire 
body. For example, a study of the cardiovascular system 
looks at the heart and all of the blood vessels in the body. 
When this is completed, the nervous system (brain, 
spinal cord, and all the nerves) might be examined in 
detail. This approach continues for the whole body until 
every system, including the nervous, skeletal, muscular, 
gastrointestinal, respiratory, lymphatic, and reproduc¬ 
tive systems, has been studied. 

Each of these approaches has benefits and deficiencies. 
The regional approach works very well if the anatomy 
course involves cadaver dissection but falls short when 
it comes to understanding the continuity of an entire 
system throughout the body. Similarly, the systemic 
approach fosters an understanding of an entire system 
throughout the body, but it is very difficult to coordinate 
this directly with a cadaver dissection or to acquire suffi¬ 
cient detail. 

Important anatomical terms 
The anatomical position 

The anatomical position is the standard reference position 
of the body used to describe the location of structures (Fig. 
1.1). The body is in the anatomical position when standing 
upright with feet together, hands by the side and face 
looking forward. The mouth is closed and the facial expres¬ 
sion is neutral. The rim of bone under the eyes is in the 
same horizontal plane as the top of the opening to the 
ear, and the eyes are open and focused on something in 
the distance. The palms of the hands face forward with the 
fingers straight and together and with the pad of the thumb 
turned 90° to the pads of the fingers. The toes point 
forward. 

Anatomical planes 

Three major groups of planes pass through the body in the 
anatomical position (Fig. 1.1). 



What is anatomy • Important Anatomical Terms 


i 




Inferior margin of orbit level with 
top of external auditory meatus 


Face looking forward 


Sagittal plane 


Anterior 


Feet together 
toes forward 


Hands by sides 
palms forward 


Transverse, horizontal, 
or axial plane 


Posterior 


Lateral 



Fig. 1.1 The anatomical position, planes, and terms of location and orientation. 


3 


















The Body 


■ Coronal planes are oriented vertically and divide the 
body into anterior and posterior parts. 

■ Sagittal planes also are oriented vertically but are at 
right angles to the coronal planes and divide the body 
into right and left parts. The plane that passes through 
the center of the body dividing it into equal right and 
left halves is termed the median sagittal plane. 

■ Transverse, horizontal, or axial planes divide the 
body into superior and inferior parts. 

Terms to describe location 

Anterior (ventral) and posterior (dorsal), 
medial and lateral, superior and inferior 

Three major pairs of terms are used to describe the location 
of structures relative to the body as a whole or to other 
structures (Fig. 1.1). 

■ Anterior (or ventral) and posterior (or dorsal) 

describe the position of structures relative to the “front” 
and “back” of the body. For example, the nose is an 
anterior (ventral) structure, whereas the vertebral 
column is a posterior (dorsal) structure. Also, the nose 
is anterior to the ears and the vertebral column is pos¬ 
terior to the sternum. 

■ Medial and lateral describe the position of structures 
relative to the median sagittal plane and the sides of 
the body. For example, the thumb is lateral to the little 
finger. The nose is in the median sagittal plane and is 
medial to the eyes, which are in turn medial to the exter¬ 
nal ears. 

■ Superior and inferior describe structures in reference 
to the vertical axis of the body. For example, the head is 
superior to the shoulders and the knee joint is inferior 
to the hip joint. 

Proximal and distal, cranial and caudal, 
and rostral 

Other terms used to describe positions include proximal 
and distal, cranial and caudal, and rostral. 


■ Proximal and distal are used with reference to being 
closer to or farther from a structure’s origin, particu¬ 
larly in the limbs. For example, the hand is distal to the 
elbow joint. The glenohumeral joint is proximal to the 
elbow joint. These terms are also used to describe 
the relative positions of branches along the course of 
linear structures, such as airways, vessels, and nerves. 
For example, distal branches occur farther away toward 
the ends of the system, whereas proximal branches 
occur closer to and toward the origin of the system. 

■ Cranial (toward the head) and caudal (toward the tail) 
are sometimes used instead of superior and inferior, 
respectively. 

■ Rostral is used, particularly in the head, to describe the 
position of a structure with reference to the nose. For 
example, the forebrain is rostral to the hindbrain. 

Superficial and deep 

Two other terms used to describe the position of structures 
in the body are superficial and deep. These terms are 
used to describe the relative positions of two structures 
with respect to the surface of the body. For example, the 
sternum is superficial to the heart, and the stomach is deep 
to the abdominal wall. 

Superficial and deep can also be used in a more absolute 
fashion to define two major regions of the body. The super¬ 
ficial region of the body is external to the outer layer of 
deep fascia. Deep structures are enclosed by this layer. 
Structures in the superficial region of the body include the 
skin, superficial fascia, and mammary glands. Deep struc¬ 
tures include most skeletal muscles and viscera. Superficial 
wounds are external to the outer layer of deep fascia, 
whereas deep wounds penetrate through it. 



Imaging • Diagnostic Imaging Techniques 


i 


Imaging 


Diagnostic imaging techniques 

In 18 9 5 Wilhelm Roentgen used the X-rays from a cathode 
ray tube to expose a photographic plate and produce the 
first radiographic exposure of his wife’s hand. Over the past 
30 years there has been a revolution in body imaging, 
which has been paralleled by developments in computer 
technology 

Plain radiography 

The basic physics of X-ray generation has not changed. 

X-rays are photons (a type of electromagnetic radiation) 
and are generated from a complex X-ray tube, which is a 
type of cathode ray tube (Fig. 1.2). The X-rays are then 
collimated (i.e., directed through lead-lined shutters to stop 
them from fanning out) to the appropriate area, as deter¬ 
mined by the radiographic technician. As the X-rays pass 
through the body they are attenuated (reduced in energy) 
by the tissues. Those X-rays that pass through the tissues 
interact with the photographic film. 

In the body: 

■ air attenuates X-rays a little; 

■ fat attenuates X-rays more than air but less than 
water; and 

■ bone attenuates X-rays the most. 

These differences in attenuation result in differences in 
the level of exposure of the film. When the photographic 
film is developed, bone appears white on the film because 
this region of the film has been exposed to the least amount 
of X-rays. Air appears dark on the film because these 
regions were exposed to the greatest number of X-rays. 

Modifications to this X-ray technique allow a continu¬ 
ous stream of X-rays to be produced from the X-ray tube 
and collected on an input screen to allow real-time visual¬ 
ization of moving anatomical structures, barium studies, 
angiography, and fluoroscopy (Fig. 1.3). 


Tungsten filament— 


— Tungsten target 


Focusing cup — 



Cathode_ 


— Glass X-ray tube 



— Anode 

X-rays 


Fig. 1.2 Cathode ray tube for the production of X-rays. 



Fig. 1.3 Fluoroscopy unit. 


5 






































The Body 


Contrast agents 

To demonstrate specific structures, such as bowel loops or 
arteries, it may be necessary to fill these structures with a 
substance that attenuates X-rays more than bowel loops or 
arteries do normally. It is, however, extremely important 
that these substances are non toxic. Barium sulfate, an 
insoluble salt, is a nontoxic, relatively high-density agent 
that is extremely useful in the examination of the gastro¬ 
intestinal tract. When barium sulfate suspension is 
ingested it attenuates X-rays and can therefore be used to 
demonstrate the bowel lumen (Fig. 1.4). It is common to 
add air to the barium sulfate suspension, by either ingest¬ 
ing “fizzy” granules or directly instilling air into the body 
cavity, as in a barium enema. This is known as a double¬ 
contrast (air/barium) study. 

For some patients it is necessary to inject contrast agents 
directly into arteries or veins. In this case, iodine-based 
molecules are suitable contrast agents. Iodine is chosen 
because it has a relatively high atomic mass and so mark¬ 
edly attenuates X-rays, but also, importantly, it is naturally 
excreted via the urinary system. Intra-arterial and intrave¬ 
nous contrast agents are extremely safe and are well toler¬ 
ated by most patients. Rarely, some patients have an 
anaphylactic reaction to intra-arterial or intravenous 



Fig. 1.4 Barium sulfate follow-through. 


injections, so the necessary precautions must be taken. 
Intra-arterial and intravenous contrast agents not only 
help in visualizing the arteries and veins but because they 
are excreted by the urinary system, can also be used to 
visualize the kidneys, ureter, and bladder in a process 
known as intravenous urography. 

Subtraction angiography 

During angiography it is often difficult to appreciate the 
contrast agent in the vessels through the overlying bony 
structures. To circumvent this, the technique of subtrac¬ 
tion angiography has been developed. Simply, one or 
two images are obtained before the injection of contrast 
media. These images are inverted (such that a negative is 
created from the positive image). After injection of the con¬ 
trast media into the vessels, a further series of images are 
obtained, demonstrating the passage of the contrast 
through the arteries into the veins and around the circula¬ 
tion. By adding the “negative precontrast image” to the 
positive postcontrast images, the bones and soft tissues 
are subtracted to produce a solitary image of contrast 
only. Before the advent of digital imaging this was a 
challenge, but now the use of computers has made this 
technique relatively straightforward and instantaneous 
(Fig. 1.5). 




Imaging • Diagnostic Imaging Techniques 


i 


Ultrasound 

Ultrasonography of the body is widely used for all aspects 
of medicine. 

Ultrasound is a very high frequency sound wave 
(not electromagnetic radiation) generated by piezoelectric 
materials, such that a series of sound waves is produced. 
Importantly, the piezoelectric material can also receive the 
sound waves that bounce back from the internal organs. 
The sound waves are then interpreted by a powerful 
computer, and a real-time image is produced on the 
display panel. 

Doppler ultrasound 

Developments in ultrasound technology, including the size 
of the probes and the frequency range, mean that a broad 
range of areas can now be scanned. 

Traditionally ultrasound is used for assessing the 
abdomen (Fig. 1.6) and the fetus in pregnant women. 
Ultrasound is also widely used to assess the eyes, neck, soft 
tissues, and peripheral musculoskeletal system. Probes 
have been placed on endoscopes, and endoluminal ultra¬ 
sound of the esophagus, stomach, and duodenum is now 
routine. Endocavity ultrasound is carried out most com¬ 
monly to assess the genital tract in women using a 
transvaginal or transrectal route. In men, transrectal 
ultrasound is the imaging method of choice to assess the 



Fig. 1.6 Ultrasound examination of the abdomen. 


prostate in those with suspected prostate hypertrophy or 
malignancy. 

Doppler ultrasound enables determination of flow, its 
direction, and its velocity within a vessel using simple 
ultrasound techniques. Sound waves bounce off moving 
structures and are returned. The degree of frequency shift 
determines whether the object is moving away from or 
toward the probe and the speed at which it is traveling. 
Precise measurements of blood flow and blood velocity can 
therefore be obtained, which in turn can indicate sites of 
blockage in blood vessels. 

Computed tomography 

Computed tomography (CT) was invented in the 1970s by 
Sir Godfrey Hounsfield, who was awarded the Nobel Prize 
in Medicine in 1979. Since this inspired invention there 
have been many generations of CT scanners. A CT scanner 
obtains a series of images of the body (slices) in the 
axial plane. 

The patient lies on a bed, an X-ray tube passes 
around the body (Fig. 1.7), and a series of images are 
obtained. A computer carries out a complex mathematical 



Fig. 1.7 Computed tomography scanner. 


7 














The Body 


transformation on the multitude of images to produce the 
final image (Fig. 1.8). 

Magnetic resonance imaging 

Nuclear magnetic resonance imaging was first described in 
1946 and used to determine the structure of complex mol¬ 
ecules. The complexity of the physics necessary to obtain 
an image is beyond the scope of this textbook, but the 
reader should be aware of how the image is produced and 
the types of images typically seen in routine medical 
practice. 

The process of magnetic resonance imaging (MRI) is 
dependent on the free protons in the hydrogen nuclei in 
molecules of water (H 2 0). Because water is present in 
almost all biological tissues, the hydrogen proton is ideal. 
The protons within a patient’s hydrogen nuclei can be 
regarded as small bar magnets, which are randomly ori¬ 
ented in space. The patient is placed in a strong magnetic 
field, which aligns the bar magnets. When a pulse of radio 
waves is passed through the patient the magnets are 
deflected, and as they return to their aligned position they 
emit small radio pulses. The strength and frequency of the 
emitted pulses and the time it takes for the protons to 
return to their pre-excited state produce a signal. These 
signals are analyzed by a powerful computer, and an image 
is created (Fig. 1.9). 

By altering the sequence of pulses to which the protons 
are subjected, different properties of the protons can be 
assessed. These properties are referred to as the “weight¬ 
ing” of the scan. By altering the pulse sequence and the 
scanning parameters, Tl-weighted images (Fig. 1.1 OA) 
and T2-weighted images (Fig. 1.10B) can be obtained. 
These two types of imaging sequences provide differences 
in image contrast, which accentuate and optimize different 
tissue characteristics. 

From the clinical point of view: 

■ Most Tl-weighted images show dark fluid and bright 
fat—for example, within the brain the cerebrospinal 
fluid (CSF) is dark; 

■ T2-weighted images demonstrate a bright signal from 
fluid and an intermediate signal from fat—for example, 
in the brain the CSF appears white. 

MRI can also be used to assess flow within vessels and 
to produce complex angiograms of the peripheral and cere¬ 
bral circulation. 

Nuclear medicine imaging 

Nuclear medicine involves imaging using gamma rays, 
8 which are another type of electromagnetic radiation. 



Fig. 1.9 A T2-weighted image in the sagittal plane of the pelvic 
viscera in a woman. 


The important difference between gamma rays and 
X-rays is that gamma rays are produced from within the 
nucleus of an atom when an unstable nucleus decays, 
whereas X-rays are produced by bombarding an atom with 
electrons. 

For an area to be visualized, the patient must receive a 
gamma ray emitter, which must have a number of proper¬ 
ties to be useful, including: 

■ a reasonable half-life (e.g., 6 to 24 hours), 

■ an easily measurable gamma ray, and 




Imaging • Nuclear Medicine Imaging 


i 



Fig. 1.10 Tl-weighted (A) and T2-weighted (B) magnetic resonance 
images of the brain in the coronal plane. 


■ energy deposition in as low a dose as possible in the 

patient’s tissues. 

The most commonly used radionuclide (radioisotope) is 
technetium-99m. This may be injected as a technetium 
salt or combined with other complex molecules. For 
example, by combining technetium-99m with methylene 
diphosphonate (MDP), a radiopharmaceutical is produced. 
When injected into the body this radiopharmaceutical spe¬ 
cifically binds to bone, allowing assessment of the skeleton. 
Similarly, combining technetium-9 9 m with other com¬ 
pounds permits assessment of other parts of the body, for 
example the urinary tract and cerebral blood flow. 

Depending on how the radiopharmaceutical is 
absorbed, distributed, metabolized, and excreted by the 
body after injection, images are obtained using a gamma 
camera (Fig. 1.11). 

Positron emission tomography 

Positron emission tomography (PET) is an imaging modal¬ 
ity for detecting positron-emitting radionuclides. A posi¬ 
tron is an anti-electron, which is a positively charged 
particle of antimatter. Positrons are emitted from the 
decay of proton-rich radionuclides. Most of these radionu¬ 
clides are made in a cyclotron and have extremely short 
half-lives. 

The most commonly used PET radionuclide is fluorode- 
oxyglucose (FDG) labeled with fluorine-18 (a positron 



Fig. 1.11 A gamma camera. 


9 









The Body 


emitter). Tissues that are actively metabolizing glucose 
take up this compound, and the resulting localized high 
concentration of this molecule compared to background 
emission is detected as a “hot spot.” 

PET has become an important imaging modality in the 
detection of cancer and the assessment of its treatment 
and recurrence. 

IMAGE INTERPRETATION 


Imaging is necessary in most clinical specialties to diag¬ 
nose pathological changes to tissues. It is paramount to 
appreciate what is normal and what is abnormal. An 
appreciation of how the image is obtained, what the 
normal variations are, and technical considerations is nec¬ 
essary to obtain a radiological diagnosis. Without under¬ 
standing the anatomy of the region imaged, it is impossible 
to comment on the abnormal. 

Plain radiography 

Plain radiographs are undoubtedly the most common form 
of image obtained in a hospital or local practice. Before 
interpretation, it is important to know about the imaging 
technique and the views obtained as standard. 

In most instances (apart from chest radiography) 
the X-ray tube is 1 m away from the X-ray film. The object 
in question, for example a hand or a foot, is placed 
upon the film. When describing subject placement for radi¬ 
ography, the part closest to the X-ray tube is referred to as 
“anterior” and that closest to the film is referred to as 
“posterior.” 

When X-rays are viewed on a viewing box, the right side 
of the patient is placed to the observer’s left; therefore, the 
observer views the radiograph as though looking at a 
patient in the anatomical position. 

Chest radiograph 

The chest radiograph is one of the most commonly 
requested plain radiographs. An image is taken with the 
patient erect and placed posteroanteriorly (PA chest 
radiograph). 

Occasionally, when patients are too unwell to stand 
erect, films are obtained on the bed in an anteroposterior 
(AP) position. These films are less standardized than PA 
films, and caution should always be taken when interpret¬ 
ing AP radiographs. 

The plain chest radiograph should always be 
checked for quality. Film markers should be placed on the 
appropriate side. (Occasionally patients have dextrocardia, 
which may be misinterpreted if the film marker is placed 


inappropriately.) A good-quality chest radiograph will 
demonstrate the lungs, cardiomediastinal contour, dia¬ 
phragm, ribs, and peripheral soft tissues. 

Abdominal radiograph 

Plain abdominal radiographs are obtained in the AP 
supine position. From time to time an erect plain abdomi¬ 
nal radiograph is obtained when small bowel obstruction 
is suspected. 

Gastrointestinal contrast examinations 

High-density contrast medium is ingested to opacify the 
esophagus, stomach, small bowel, and large bowel. As 
described previously (p. 6), the bowel is insufflated with air 
(or carbon dioxide) to provide a double-contrast study. In 
many countries, endoscopy has superseded upper gastro¬ 
intestinal imaging, but the mainstay of imaging the large 
bowel is the double-contrast barium enema. Typically the 
patient needs to undergo bowel preparation, in which pow¬ 
erful cathartics are used to empty the bowel. At the time of 
the examination a small tube is placed into the rectum and 
a barium suspension is run into the large bowel. The 
patient undergoes a series of twists and turns so that the 
contrast passes through the entire large bowel. The con¬ 
trast is emptied and air is passed through the same tube to 
insufflate the large bowel. A thin layer of barium coats the 
normal mucosa, allowing mucosal detail to be visualized 
(see Fig. 1.4). 

Urological contrast studies 

Intravenous urography is the standard investigation for 
assessing the urinary tract. Intravenous contrast medium 
is injected, and images are obtained as the medium is 
excreted through the kidneys. A series of films are obtained 
during this period from immediately after the injection up 
to approximately 20 minutes later, when the bladder is full 
of contrast medium. 

This series of radiographs demonstrates the kidneys, 
ureters, and bladder and enables assessment of the retro- 
peritoneum and other structures that may press on the 
urinary tract. 

Computed tomography 

Computed tomography is the preferred terminology rather 
than computerized tomography, though both terms are 
used interchangeably by physicians. 

The general principles of computed tomography are 
described on p. 7. It is important for the student to under¬ 
stand the presentation of images. Most images are acquired 
in the axial plane and viewed such that the observer looks 


10 



Imaging • Safety In Imaging 


from below and upward toward the head (from the foot of 
the bed). By implication: 

■ the right side of the patient is on the left side of the 
image, and 

■ the uppermost border of the image is anterior. 

Many patients are given oral and intravenous contrast 
media to differentiate bowel loops from other abdominal 
organs and to assess the vascularity of normal anatomical 
structures. When intravenous contrast is given, the earlier 
the images are obtained, the greater the likelihood of arte¬ 
rial enhancement. As the time is delayed between injection 
and image acquisition, a venous phase and an equilibrium 
phase are also obtained. 

The great advantage of CT scanning is the ability to 
extend and compress the gray scale to visualize the bones, 
soft tissues, and visceral organs. Altering the window set¬ 
tings and window centering provides the physician with 
specific information about these structures. 

Magnetic resonance imaging 

There is no doubt that MRI has revolutionized the under¬ 
standing and interpretation of the brain and its coverings. 
Furthermore, it has significantly altered the practice of 
musculoskeletal medicine and surgery. Images can be 
obtained in any plane and in most sequences. Typically the 
images are viewed using the same principles as CT. Intrave¬ 
nous contrast agents are also used to further enhance tissue 
contrast. Typically, MRI contrast agents contain paramag¬ 
netic substances (e.g., gadolinium and manganese). 

Nuclear medicine imaging 

Most nuclear medicine images are functional studies. 
Images are usually interpreted directly from a computer, 
and a series of representative films are obtained for 
clinical use. 


SAFETY INJMAGING 

Whenever a patient undergoes an X-ray or nuclear medi¬ 
cine investigation, a dose of radiation is given (Table 1.1). 
Asa general principle it is expected that the dose given is 
as low as reasonably possible for a diagnostic image to be 
obtained. Numerous laws govern the amount of radiation 
exposure that a patient can undergo for a variety of proce¬ 
dures, and these are monitored to prevent any excess or 
additional dosage. Whenever a radiograph is booked, the 
clinician ordering the procedure must appreciate its neces¬ 
sity and understand the dose given to the patient to ensure 
that the benefits significantly outweigh the risks. 

Imaging modalities such as ultrasound and MRI are 
ideal because they do not impart significant risk to the 
patient. Moreover, ultrasound imaging is the modality of 
choice for assessing the fetus. 

Any imaging device is expensive, and consequently 
the more complex the imaging technique (e.g., MRI) the 
more expensive the investigation. Investigations must be 
carried out judiciously, based on a sound clinical history 
and examination, for which an understanding of anatomy 
is vital. 


Table 1.1 The approximate dosage of radiation exposure 


as an order of magnitude 


Examination 

Typical 
effective 
dose (mSv) 

Equivalent duration 
of background 
exposure 

Chest radiograph 

0.02 

3 days 

Abdomen 

1.00 

6 months 

Intravenous urography 

2.50 

14 months 

CT scan of head 

2.30 

1 year 

CT scan of abdomen 
and pelvis 

10.00 

4.5 years 



The Body 


Body systems 


SKELETAL SYSTEM 


The skeleton can be divided into two subgroups, the axial 
skeleton and the appendicular skeleton. The axial skeleton 
consists of the bones of the skull (cranium), vertebral 
column, ribs, and sternum, whereas the appendicular skel¬ 
eton consists of the bones of the upper and lower limbs 
(Fig. 1.12). 

The skeletal system consists of cartilage and bone. 


Cartilage 

Cartilage is an avascular form of connective tissue consist¬ 
ing of extracellular fibers embedded in a matrix that con¬ 
tains cells localized in small cavities. The amount and kind 
of extracellular fibers in the matrix varies depending on the 
type of cartilage. In heavy weightbearing areas or areas 
prone to pulling forces, the amount of collagen is greatly 
increased and the cartilage is almost inextensible. In con¬ 
trast, in areas where weightbearing demands and stress are 
less, cartilage containing elastic fibers and fewer collagen 
fibers is common. The functions of cartilage are to: 

■ support soft tissues, 

■ provide a smooth, gliding surface for bone articulations 
at joints, and 

■ enable the development and growth of long bones. 
There are three types of cartilage: 

■ hyaline—most common; matrix contains a moderate 
amount of collagen fibers (e.g., articular surfaces of 
bones); 

■ elastic—matrix contains collagen fibers along with a 
large number of elastic fibers (e.g., external ear); 

■ fibrocartilage—matrix contains a limited number of 
cells and ground substance amidst a substantial amount 
of collagen fibers (e.g., intervertebral discs). 

Cartilage is nourished by diffusion and has no blood 
vessels, lymphatics, or nerves. 



Fig. 1.12 The axial skeleton and the appendicular skeleton. 


12 


□ □ 














Body systems • Skeletal System 


Bone 

Bone is a calcified, living, connective tissue that forms the 
majority of the skeleton. It consists of an intercellular cal¬ 
cified matrix, which also contains collagen fibers, and 
several types of cells within the matrix. Bones function as: 

■ supportive structures for the body, 

■ protectors of vital organs, 

■ reservoirs of calcium and phosphorus, 

■ levers on which muscles act to produce movement, and 

■ containers for blood-producing cells. 

There are two types of bone, compact and spongy (tra¬ 
becular or cancellous). Compact bone is dense bone that 
forms the outer shell of all bones and surrounds spongy 
bone. Spongy bone consists of spicules of bone enclosing 
cavities containing blood-forming cells (marrow). Classifi¬ 
cation of bones is by shape. 

■ Long bones are tubular (e.g., humerus in upper limb; 
femur in lower limb). 

■ Short bones are cuboidal (e.g., bones of the wrist and 
ankle). 

■ Flat bones consist of two compact bone plates separated 
by spongy bone (e.g., skull). 

■ Irregular bones are bones with various shapes (e.g., 
bones of the face). 


■ Sesamoid bones are round or oval bones that develop in 

tendons. 

Bones are vascular and are innervated. Generally, an 
adjacent artery gives off a nutrient artery, usually one per 
bone, that directly enters the internal cavity of the bone 
and supplies the marrow, spongy bone, and inner layers of 
compact bone. In addition, all bones are covered externally, 
except in the area of a joint where articular cartilage is 
present, by a fibrous connective tissue membrane called the 
periosteum, which has the unique capability of forming 
new bone. This membrane receives blood vessels whose 
branches supply the outer layers of compact bone. A bone 
stripped of its periosteum will not survive. Nerves accom¬ 
pany the vessels that supply the bone and the periosteum. 
Most of the nerves passing into the internal cavity with the 
nutrient artery are vasomotor fibers that regulate blood 
flow. Bone itself has few sensory nerve fibers. On the other 
hand, the periosteum is supplied with numerous sensory 
nerve fibers and is very sensitive to any type of injury. 

Developmentally, all bones come from mesenchyme by 
either intramembranous ossification, in which mesenchy¬ 
mal models of bones undergo ossification, or endochondral 
ossification, in which cartilaginous models of bones form 
from mesenchyme and undergo ossification. 


The Body 


In the clinic 

Determination of skeletal age 

Throughout life the bones develop in a predictable way to 
form the skeletally mature adult at the end of puberty. In 
western countries skeletal maturity tends to occur 
between the ages of 20 and 25 years. However, this may 
well vary according to geography and socioeconomic 
conditions. Skeletal maturity will also be determined by 
genetic factors and disease states. 

Up until the age of skeletal maturity, bony growth and 
development follows a typically predictable ordered state, 
which can be measured through either ultrasound, plain 
radiographs, or MRI scanning. Typically, the nondominant 


(left) hand is radiographed, and the radiograph is 
compared to a series of standard radiographs. From these 
images the bone age can be determined (Fig. 1.13). 

In certain disease states, such as malnutrition and 
hypothyroidism, bony maturity may be slow. If the skeletal 
bone age is significantly reduced from the patient's true 
age, treatment may be required. 

In the healthy individual the bone age accurately 
represents the true age of the patient. This is important in 
determining the true age of the subject. This may also 
have medicolegal importance. 



14 


Fig. 1.13 A developmental series of radiographs showing the progressive ossification of carpal (wrist) bones from 3 (A) to 10 (D) years 
of age. 


Body systems • Skeletal System 


In the clinic 


Bone marrow transplants 

The bone marrow serves an important function. There are 
two types of bone marrow, the red marrow (otherwise 
known as myeloid tissue) and the yellow marrow. Red 
blood cells, platelets, and most white blood cells arise 
from within the red marrow. In the yellow marrow a few 
white cells are made; however this marrow is dominated 
by large fat globules (producing its yellow appearance) 
(Fig. 1.14). 

From birth most of the body's marrow is red; however, 
as the subject ages, more red marrow is converted into 
yellow marrow within the medulla of the long and 
flat bones. 

Bone marrow contains two types of stem cells. 
Hemopoietic stem cells give rise to the white blood cells, 
red blood cells, and platelets. Mesenchymal stem cells 
differentiate into structures that form bone, cartilage, 
and muscle. 

There are a number of diseases that may involve the 
bone marrow, including infection and malignancy. In 
patients who develop a bone marrow malignancy (e.g., 
leukemia) it may be possible to harvest nonmalignant 
cells from the patient's bone marrow or cells from another 
person's bone marrow. The patient's own marrow can be 
destroyed with chemotherapy or radiation and the new 
cells infused. This treatment is bone marrow 
transplantation. 


Red marrow in body 
of lumbar vertebra 



Fig. 1.14 Tl-weighted image in the coronal plane, 
demonstrating the relatively high signal intensity returned 
from the femoral heads and proximal femoral necks, 
consistent with yellow marrow. In this young patient, the 
vertebral bodies return an intermediate darker signal that 
represents red marrow. There is relatively little fat in these 
vertebrae; hence the lower signal return. 



The Body 


In the clinic 
Bone fractures 

Fractures occur in normal bone because of abnormal load 
or stress, in which the bone gives way. Fractures may also 
occur in bone that is of poor quality (osteoporosis); in 
such cases a normal stress is placed upon a bone that is 
not of sufficient quality to withstand this force and 
subsequently fractures. 

In children whose bones are still developing, fractures 
may occur across the growth plate or across the shaft. 
These shaft fractures typically involve partial cortical 
disruption, similar to breaking a branch of a young tree; 
hence they are termed "greenstick" fractures (Fig. 1.15). 

After a fracture has occurred, the natural response is to 
heal the fracture. Between the fracture margins a blood 
clot is formed into which new vessels grow. A jelly-like 
matrix is formed, and further migration of collagen- 
producing cells occurs. On this soft tissue framework, 
calcium hydroxyapatite is produced by osteoblasts and 
forms insoluble crystals, and then bone matrix is laid 
down. As more bone is produced, a callus can be 
demonstrated forming across the fracture site. 

Treatment of fractures requires a fracture line 
reduction. If this cannot be maintained in a plaster of Paris 
cast, it may require internal or external fixation with 
screws and metal rods. 


Radius—v Radial epiphysis 



Fig. 1.15 Radiograph, lateral view, showing greenstick fractures 
of the distal radius and distal ulna. 


In the clinic 
Avascular necrosis 

Avascular necrosis is cellular death of bone resulting from 
a temporary or permanent loss of blood supply to that 
bone. Avascular necrosis may occur in a variety of medical 
conditions, some of which have an etiology that is less 
than clear. A typical site for avascular necrosis is a fracture 
across the femoral neck in an elderly patient. In these 
patients there is loss of continuity of the cortical 
medullary blood flow with loss of blood flow deep to the 
retinacular fibers. This essentially renders the femoral 
head bloodless; it subsequently undergoes necrosis and 
collapses. In these patients it is necessary to replace the 
femoral head with a prosthesis (Fig. 1.16). 


r Wasting of gluteal muscle 



Avascular necrosis - 1 


Bladder 


L Normal left hip 


Fig. 1.16 Image of the hip joints demonstrating loss of height 
of the right femoral head with juxta-articular bony sclerosis 
and subchondral cyst formation secondary to avascular 
necrosis. There is also significant wasting of the muscles 
supporting the hip, which is secondary to disuse and pain. 








Body systems • Skeletal System 


In the clinic 
Osteoporosis 

Osteoporosis is a disease in which the bone mineral 
density is significantly reduced. This renders the bone 
significantly more at risk of fracture. Typically, 
osteoporotic fractures occur in the femoral necks, the 
vertebrae, and the wrist. Although osteoporosis may occur 
in men, especially elderly men, the typical patients are 
postmenopausal women. There are a number of risk 



-Wedge fracture 

Fig. 1.17 Radiograph of the lumbar region of the vertebral 
column demonstrating a wedge fracture of the LI vertebra. 
This condition is typically seen in patients with osteoporosis. 


factors that predispose bones to develop osteoporosis. 
These factors include poor diet, steroid usage, smoking, 
and premature ovarian failure. Treatment involves 
removing underlying potentiating factors, such as 
improving diet and preventing further bone loss with 
drug treatment (e.g., vitamin D and calcium supplements; 
newer treatments include drugs that increase bone 
mineral density) (Figs. 1.17 and 1.18). 



Fig. 1.18 Radiograph of the lumbar region of the vertebral 
column demonstrating three intrapedicular needles, all of 
which have been placed into the middle of the vertebral 
bodies. The high-density material is radiopaque bone cement, 
which has been injected as a liquid that will harden. 









The Body 


In the clinic 
Epiphyseal fractures 

As the skeleton develops, there are stages of intense 
growth typically around the ages of 7 to 10 years and 
later in puberty. These growth spurts are associated 
with increased cellular activity around the growth plate 
and the metaphyseal region. This increase in activity 
renders the growth plates and metaphyseal regions 
more vulnerable to injuries, which may occur from 
dislocation across a growth plate or fracture through 
a growth plate. Occasionally an injury may result in 
growth plate compression, destroying that region of the 
growth plate, which may result in asymmetrical growth 
across that joint region. All fractures across the growth 
plate must be treated with care and expediency, 
requiring fracture reduction. 


Joints 

The sites where two skeletal elements come together 
are termed joints. The two general categories of joints 
(Fig. 1.19) are those in which: 

■ the skeletal elements are separated by a cavity (i.e., 

synovial joints), and 

■ there is no cavity and the components are held together 
by connective tissue (i.e., solid joints). 

Blood vessels that cross a joint and nerves that inner¬ 
vate muscles acting on a joint usually contribute articular 
branches to that joint. 

Synovial joints 

Synovial joints are connections between skeletal compo¬ 
nents where the elements involved are separated by a 
narrow articular cavity (Fig. 1.20). In addition to contain¬ 
ing an articular cavity, these joints have a number of char¬ 
acteristic features. 

First, a layer of cartilage, usually hyaline cartilage, 
covers the articulating surfaces of the skeletal elements. In 
other words, bony surfaces do not normally contact one 
another directly. As a consequence, when these joints are 
viewed in normal radiographs, a wide gap seems to sepa¬ 
rate the adjacent bones because the cartilage that covers 
the articulating surfaces is more transparent to X-rays 
than bone. 

A second characteristic feature of synovial joints is the 
presence of a joint capsule consisting of an inner syno- 
1 8 vial membrane and an outer fibrous membrane. 




- - j 




:::: 




Bone Connective tissue Bone 

B Solid joint 

Fig. 1.19 Joints. A. Synovial joint. B. Solid joint. 


■ The synovial membrane attaches to the margins of the 
joint surfaces at the interface between the cartilage and 
bone and encloses the articular cavity. The synovial 
membrane is highly vascular and produces synovial 
fluid, which percolates into the articular cavity and 
lubricates the articulating surfaces. Closed sacs of syno¬ 
vial membrane also occur outside joints, where they 
form synovial bursae or tendon sheaths. Bursae often 
intervene between structures, such as tendons and 
bone, tendons and joints, or skin and bone, and reduce 
the friction of one structure moving over the other. 
Tendon sheaths surround tendons and also reduce 
friction. 

■ The fibrous membrane is formed by dense connective 
tissue and surrounds and stabilizes the joint. Parts of 
the fibrous membrane may thicken to form ligaments, 
which further stabilize the joint. Ligaments outside the 
capsule usually provide additional reinforcement. 

Another common but not universal feature of synovial 
joints is the presence of additional structures within the 
area enclosed by the capsule or synovial membrane, such 
as articular discs (usually composed of fibrocartilage), 
fat pads, and tendons. Articular discs absorb compres¬ 
sion forces, adjust to changes in the contours of joint sur¬ 
faces during movements, and increase the range of 
movements that can occur at joints. Fat pads usually occur 
between the synovial membrane and the capsule and move 


























Body systems • Skeletal System 


Tendon 




Hyaline 

cartilage 


Sheath 


Articular cavity 

A 

Fig. 1.20 Synovial joints. A. Major features of a 


Joint 

capsule 


Fibrous 

membrane 


Articular 

disc 


B Skin Bursa 

synovial joint. B. Accessory structures associated with synovial joints. 


Fibrous 
membrane 

Synovial 

membrane 


Fat pad 


— Synovial 
membrane 


Hyaline cartilage 


into and out of regions as joint contours change during 
movement. Redundant regions of the synovial membrane 
and fibrous membrane allow for large movements at joints. 

Descriptions of synovial joints based on shape 
and movement 

Synovial joints are described based on shape and 
movement: 

■ based on the shape of their articular surfaces, synovial 
joints are described as plane (flat), hinge, pivot, 


bicondylar (two sets of contact points), condylar (ellip¬ 
soid), saddle, and ball and socket; 

■ based on movement, synovial joints are described as 
uniaxial (movement in one plane), biaxial (movement 
in two planes), and multiaxial (movement in three 
planes). 

Hinge joints are uniaxial, whereas ball and socket joints 
are multiaxial. 

















The Body 


Specific types of synovial joints 
(Fig. 1.21) 

■ Plane joints—allow sliding or gliding movements when 
one bone moves across the surface of another (e.g., 
acromioclavicular joint) 

■ Hinge joints—allow movement around one axis that 
passes transversely through the joint; permit flexion and 
extension (e.g., elbow [humero-ulnar] joint) 

■ Pivot joints—allow movement around one axis that 
passes longitudinally along the shaft of the bone; permit 
rotation (e.g., atlanto-axial joint) 

■ Bicondylar joints—allow movement mostly in one axis 
with limited rotation around a second axis; formed by 
two convex condyles that articulate with concave or flat 
surfaces (e.g., knee joint) 

■ Condylar (ellipsoid) joints—allow movement around 
two axes that are at right angles to each other; permit 
flexion, extension, abduction, adduction, and circum¬ 
duction (limited) (e.g., wrist joint) 

■ Saddle joints—allow movement around two axes that 
are at right angles to each other; the articular surfaces 
are saddle shaped; permit flexion, extension, abduction, 
adduction, and circumduction (e.g., carpometacarpal 
joint of the thumb) 

■ Ball and socket joints—allow movement around 
multiple axes; permit flexion, extension, abduction, 


adduction, circumduction, and rotation (e.g., hip 
joint) 

Solid joints 

Solid joints are connections between skeletal elements 
where the adjacent surfaces are linked together either 
by fibrous connective tissue or by cartilage, usually fibro- 
cartilage (Fig. 1.22). Movements at these joints are more 
restricted than at synovial joints. 

Fibrous joints include sutures, gomphoses, and 
syndesmoses. 

■ Sutures occur only in the skull where adjacent bones 
are linked by a thin layer of connective tissue termed a 
sutural ligament. 

■ Gomphoses occur only between the teeth and adjacent 
bone. In these joints, short collagen tissue fibers in the 
periodontal ligament run between the root of the tooth 
and the bony socket. 

■ Syndesmoses are joints in which two adjacent bones 
are linked by a ligament. Examples are the ligamentum 
flavum, which connects adjacent vertebral laminae, 
and an interosseous membrane, which links, for 
example, the radius and ulna in the forearm. 

Cartilaginous joints include synchondroses and 
symphyses. 






Humerus 


Ulna 


Odontoid process 
of axis 


Femur 


Radius 


Synovial membrane 


Articular disc 


A Synovial cavity 


Wrist joint 


Olecranon 


Ulna 


Trapezium 


Metacarpal I 


Synovial 

membrane 


Atlas 


Radius 


Cartilage 


Synovial membrane 


Fig. 1.21 Various types of synovial joints. A. Condylar (wrist). B. Gliding (radio-ulnar). C. Hinge or ginglymus (elbow). D. Ball and socket (hip). 
E. Saddle (carpometacarpal of thumb). F. Pivot (atlanto-axial). 














Body systems • Skeletal System 



■ Synchondroses occur where two ossification centers 
in a developing bone remain separated by a layer of 
cartilage, for example, the growth plate that occurs 
between the head and shaft of developing long bones. 
These joints allow bone growth and eventually become 
completely ossified. 


■ Symphyses occur where two separate bones are inter¬ 
connected by cartilage. Most of these types of joints 
occur in the midline and include the pubic symphysis 
between the two pelvic bones, and intervertebral discs 
between adjacent vertebrae. 




















































g|| The Bod V 


In the clinic 


Degenerative joint disease 

Degenerative joint disease is commonly known as 
osteoarthritis or osteoarthrosis. The disorder is related to 
aging but not caused by aging. Typically there are 
decreases in water and proteoglycan content within the 
cartilage. The cartilage becomes more fragile and more 
susceptible to mechanical disruption (Fig. 1.23). As the 
cartilage wears, the underlying bone becomes fissured 
and also thickens. Synovial fluid may be forced into small 
cracks that appear in the bone's surface, which produces 
large cysts. Furthermore, reactive juxta-articular bony 
nodules are formed (osteophytes) (Fig. 1.24). As these 
processes occur, there is slight deformation, which alters 
the biomechanical forces through the joint. This in turn 
creates abnormal stresses, which further disrupt the joint. 

In the United States, osteoarthritis accounts for up to 
one-quarter of primary health care visits and is regarded 
as a significant problem. 

The etiology of osteoarthritis is not clear; however, 
osteoarthritis can occur secondary to other joint diseases, 
such as rheumatoid arthritis and infection. Overuse of 
joints and abnormal strains, such as those experienced by 



people who play sports, often cause one to be more 
susceptible to chronic joint osteoarthritis. 

Various treatments are available, including weight 
reduction, proper exercise, anti-inflammatory drug 
treatment, and joint replacement (Fig. 1.25). 



Fig. 1.23 This operative photograph demonstrates the focal 
areas of cartilage loss in the patella and femoral condyles 
throughout the knee joint. 


Fig. 1.24 This radiograph demonstrates the loss of joint space 
in the medial compartment and presence of small spiky 
osteophytic regions at the medial lateral aspect of the joint. 


22 














Body systems • Skeletal System 


In the clinic—cont'd 



Arthroscopy 

Arthroscopy is a technique of visualizing the inside of a 
joint using a small telescope placed through a tiny 
incision in the skin. Arthroscopy can be performed in most 
joints. However, it is most commonly performed in the 
knee, shoulder, ankle, and hip joints. The elbow joint and 
wrist joint can also be viewed through the arthroscope. 

Arthroscopy allows the surgeon to view the inside of 
the joint and its contents. Notably, in the knee, the 
menisci and the ligaments are easily seen, and it is 
possible using separate puncture sites and specific 
instruments to remove the menisci and replace the 
cruciate ligaments. The advantages of arthroscopy are 
that it is performed through small incisions, it enables 
patients to quickly recover and return to normal activity, 
and it only requires either a light anesthetic or regional 
anesthesia during the procedure. 


Fig. 1.25 After knee replacement. This radiograph shows the 
position of the prosthesis. 



The Body 


In the clinic 
Joint replacement 

Joint replacement is undertaken for a variety of reasons. 
These predominantly include degenerative joint disease 
and joint destruction. Joints that have severely 
degenerated or lack their normal function are painful, 
which can be life limiting, and in otherwise fit and healthy 
individuals can restrict activities of daily living. In some 
patients the pain may be so severe that it prevents them 
from leaving the house and undertaking even the smallest 
of activities without discomfort. 

Large joints are commonly affected, including the hip, 
knee, and shoulder. However, with ongoing developments 
in joint replacement materials and surgical techniques, 
even small joints of the fingers can be replaced. 

Typically, both sides of the joint are replaced; in the hip 
joint the acetabulum will be reamed, and a plastic or 
metal cup will be introduced. The femoral component will 
be fitted precisely to the femur and cemented in place 
(Fig. 1.26). 

Most patients derive significant benefit from joint 
replacement and continue to lead an active life afterward. 


SKIN AND FASCIAS 
Skin 

The skin is the largest organ of the body. It consists of the 
epidermis and the dermis. The epidermis is the outer cel¬ 
lular layer of stratified squamous epithelium, which is 
avascular and varies in thickness. The dermis is a dense bed 
of vascular connective tissue. 

The skin functions as a mechanical and permeability 
barrier, and as a sensory and thermoregulatory organ. It 
also can initiate primary immune responses. 

Fascia 

Fascia is connective tissue containing varying amounts of 
fat that separate, support, and interconnect organs and 
structures, enable movement of one structure relative to 
another, and allow the transit of vessels and nerves from 
one area to another. There are two general categories of 
24 fascia: superficial and deep. 



Artificial femoral head Acetabulum 


Fig. 1.26 This is a radiograph, anteroposterior view, of the 
pelvis after a right total hip replacement. There are additional 
significant degenerative changes in the left hip joint, which will 
also need to be replaced. 


Superficial (subcutaneous) fascia lies just deep to and is 
attached to the dermis of the skin. It is made up of loose 
connective tissue usually containing a large amount of 
fat. The thickness of the superficial fascia (subcutane¬ 
ous tissue) varies considerably, both from one area of 
the body to another and from one individual to another. 
The superficial fascia allows movement of the skin over 
deeper areas of the body, acts as a conduit for vessels and 
nerves coursing to and from the skin, and serves as an 
energy (fat) reservoir. 

Deep fascia usually consists of dense, organized connec¬ 
tive tissue. The outer layer of deep fascia is attached to 
the deep surface of the superficial fascia and forms a 
thin fibrous covering over most of the deeper region of 
the body. Inward extensions of this fascial layer form 
intermuscular septa that compartmentalize groups of 
muscles with similar functions and innervations. Other 
extensions surround individual muscles and groups of 
vessels and nerves, forming an investing fascia. Near 
some joints the deep fascia thickens, forming retinacula. 






Body systems • Muscular System 


These fascial retinacula hold tendons in place and 
prevent them from bowing during movements at the 
joints. Finally, there is a layer of deep fascia separating 
the membrane lining the abdominal cavity (the parietal 
peritoneum) from the fascia covering the deep surface 
of the muscles of the abdominal wall (the transversalis 
fascia). This layer is referred to as extraperitoneal 
fascia. A similar layer of fascia in the thorax is termed 
the endothoracic fascia. 


In the clinic 

The importance of fascias 

A fascia is a thin band of tissue that surrounds muscles, 
bones, organs, nerves, and blood vessels and often 
remains uninterrupted as a three-dimensional structure 
between tissues. It provides important support for 
tissues and can provide a boundary between structures. 

Fascias have specific dynamic properties and may be 
relatively elastic where necessary. They contain small 
blood vessels and tissue receptors and can respond to 
injury like any other tissue. 

Clinically, fascias are extremely important because 
they often limit the spread of infection and malignant 
disease. When infections or malignant diseases cross a 
fascial plain, a primary surgical clearance may require a 
far more extensive dissection to render the area free of 
tumor or infection. 

A typical example of a fascial layer would be that 
covering the psoas muscle. Infection within an 
intervertebral body secondary to tuberculosis can pass 
laterally into the psoas muscle. Pus fills the psoas 
muscle but is limited from further spread by the psoas 
fascia, which surrounds the muscle and extends 
inferiorly into the groin pointing below the inguinal 
ligament. 


MUSCULAR SYSTEM 

The muscular system is generally regarded as consisting of 
one type of muscle found in the body—skeletal muscle. 
However, there are two other types of muscle tissue found 
in the body, smooth muscle and cardiac muscle, that are 
important components of other systems. These three types 
of muscle can be characterized by whether they are con¬ 
trolled voluntarily or involuntarily, whether they appear 
striated (striped) or smooth, and whether they are associ¬ 
ated with the body wall (somatic) or with organs and blood 
vessels (visceral). 

■ Skeletal muscle forms the majority of the muscle tissue 
in the body. It consists of parallel bundles of long, mul- 
tinucleated fibers with transverse stripes, is capable of 
powerful contractions, and is innervated by somatic and 
branchial motor nerves. This muscle is used to move 
bones and other structures, and provides support and 
gives form to the body. Individual skeletal muscles are 
often named on the basis of shape (e.g., rhomboid major 
muscle), attachments (e.g., sternohyoid muscle), func¬ 
tion (e.g., flexor pollicis longus muscle), position (e.g., 
palmar interosseous muscle), or fiber orientation (e.g., 
external oblique muscle). 

■ Cardiac muscle i s striated muscle found only i n the walls 
of the heart (myocardium) and in some of the large 
vessels close to where they join the heart. It consists of 
a branching network of individual cells linked electri¬ 
cally and mechanically to work as a unit. Its contrac¬ 
tions are less powerful than those of skeletal muscle and 
it is resistant to fatigue. Cardiac muscle is innervated by 
visceral motor nerves. 

■ Smooth muscle (absence of stripes) consists of elon¬ 
gated or spindle-shaped fibers capable of slow and sus¬ 
tained contractions. It is found in the walls of blood 
vessels (tunica media), associated with hair follicles in 
the skin, located in the eyeball, and found in the walls 
of various structures associated with the gastrointesti¬ 
nal, respiratory, genitourinary, and urogenital systems. 
Smooth muscle is innervated by visceral motor nerves. 




The Body 


In the clinic 
Muscle paralysis 

Muscle paralysis is the inability to move a specific 
muscle or muscle group and may be associated with 
other neurological abnormalities, including loss of 
sensation. Paralysis may be due to abnormalities in the 
brain, the spinal cord, and the nerves supplying the 
muscles. Major causes include stroke, trauma, 
poliomyelitis, and iatrogenic factors. 

In the long term, muscle paralysis will produce 
secondary muscle wasting and overall atrophy of the 
region due to disuse. 


In the clinic 
Muscle atrophy 

Muscle atrophy is a wasting disorder of muscle. It can 
be produced by a variety of causes, which include nerve 
damage to the muscle and disuse. 

Muscle atrophy is an important problem in patients 
who have undergone long-term rest or disuse, requiring 
extensive rehabilitation and muscle building exercises 
to maintain normal activities of daily living. 


In the clinic 


Muscle injuries and strains 

Muscle injuries and strains tend to occur in specific muscle 
groups and usually are related to a sudden exertion and 
muscle disruption. They typically occur in athletes. 

Muscle tears may involve a small interstitial injury up to 
a complete muscle disruption (Fig. 1.27). It is important to 


identify which muscle groups are affected and the extent 
of the tear to facilitate treatment and obtain a prognosis, 
which will determine the length of rehabilitation 
necessary to return to normal activity. 



Fig. 1.27 Axial inversion recovery series, which 
suppresses fat and soft tissue and leaves high 
signal intensity where fluid is seen. A muscle 
tear in the right adductor longus with edema 
in and around the muscle is shown. 


26 




Body systems • Cardiovascular System 


CARDIOVASCULAR SYSTEM 

The cardiovascular system consists of the heart, which 
pumps blood throughout the body, and the blood vessels, 
which are a closed network of tubes that transport the 
blood. There are three types of blood vessels: 

■ arteries, which transport blood away from the heart; 

■ veins, which transport blood toward the heart; 

■ capillaries, which connect the arteries and veins, are the 
smallest of the blood vessels and are where oxygen, 
nutrients, and wastes are exchanged within the tissues. 

The walls of the blood vessels of the cardiovascular 
system usually consist of three layers or tunics: 

■ tunica externa (adventitia)—the outer connective tissue 
layer, 

tunica media—the middle smooth muscle layer (may 
also contain varying amounts of elastic fibers in medium 
and large arteries), and 

■ tunica intima—the inner endothelial lining of the blood 
vessels. 

Arteries are usually further subdivided into three 
classes, according to the variable amounts of smooth 
muscle and elastic fibers contributing to the thickness of 
the tunica media, the overall size of the vessel, and its 
function. 

■ Large elastic arteries contain substantial amounts of 
elastic fibers in the tunica media, allowing expansion 
and recoil during the normal cardiac cycle. This helps 
maintain a constant flow of blood during diastole. 
Examples of large elastic arteries are the aorta, the bra¬ 
chiocephalic trunk, the left common carotid artery, the 
left subclavian artery, and the pulmonary trunk. 

■ Medium muscular arteries are composed of a tunica 
media that contains mostly smooth muscle fibers. This 
characteristic allows these vessels to regulate their 
diameter and control the flow of blood to different parts 
of the body. Examples of medium muscular arteries are 
most of the named arteries, including the femoral, axil¬ 
lary, and radial arteries. 

■ Small arteries and arterioles control the filling of the 
capillaries and directly contribute to the arterial pres¬ 
sure in the vascular system. 

Veins also are subdivided into three classes. 

■ Large veins contain some smooth muscle in the tunica 
media, but the thickest layer is the tunica externa. 


Examples of large veins are the superior vena cava, the 
inferior vena cava, and the portal vein. 

■ Small and medium veins contain small amounts of 
smooth muscle, and the thickest layer is the tunica 
externa. Examples of small and medium veins are 
superficial veins in the upper and lower limbs and 
deeper veins of the leg and forearm. 

■ Venules are the smallest veins and drain the 
capillaries. 

Although veins are similar in general structure to arter¬ 
ies, they have a number of distinguishing features. 

■ The walls of veins, specifically the tunica media, are 
thin. 

■ The luminal diameters of veins are large. 

■ There often are multiple veins (venae comitantes) closely 
associated with arteries in peripheral regions. 

■ Valves often are present in veins, particularly in periph¬ 
eral vessels inferior to the level of the heart. These are 
usually paired cusps that facilitate blood flow toward 
the heart. 

More specific information about the cardiovascular 
system and how it relates to the circulation of blood 
throughout the body will be discussed, where appropriate, 
in each of the succeeding chapters of the text. 


In the clinic 
Atherosclerosis 

Atherosclerosis is a disease that affects arteries. There is 
a chronic inflammatory reaction in the walls of the 
arteries, with deposition of cholesterol and fatty 
proteins. This may in turn lead to secondary 
calcification, with reduction in the diameter of the 
vessels impeding distal flow. The plaque itself may be a 
site for attraction of platelets that may "fall off" 
(embolize) distally. Plaque Assuring may occur, which 
allows fresh clots to form and occlude the vessel. 

The importance of atherosclerosis and its effects 
depend upon which vessel is affected. If atherosclerosis 
occurs in the carotid artery, small emboli may form and 
produce a stroke. In the heart, plaque Assuring may 
produce an acute vessel thrombosis, producing a 
myocardial infarction (heart attack). In the legs, chronic 
narrowing of vessels may limit the ability of the patient 
to walk and ultimately cause distal ischemia and 
gangrene of the toes. 


27 



Li 

The Body 


In the clinic 


Varicose veins 

Varicose veins are tortuous dilated veins that typically 
occur in the legs, although they may occur in the 
superficial veins of the arm and in other organs. 

In normal individuals the movement of adjacent leg 
muscles pumps the blood in the veins to the heart. Blood 
is also pumped from the superficial veins through the 
investing layer of fascia of the leg into the deep veins. 
Valves in these perforating veins may become damaged, 
allowing blood to pass in the opposite direction. This 
increased volume and pressure produces dilatation and 
tortuosity of the superficial veins (Fig. 1.28). Apart from 
the unsightliness of larger veins, the skin may become 
pigmented and atrophic with a poor response to tissue 
damage. In some patients even small trauma may produce 
skin ulceration, which requires elevation of the limb and 
application of pressure bandages to heal. 

Treatment of varicose veins depends on their location, 
size, and severity. Typically the superficial varicose veins 
can be excised and stripped, allowing blood only to drain 
into the deep system. 


Varicose veins — 



Fig. 1.28 Photograph demonstrating varicose veins. 


In the clinic 

Anastomoses and collateral circulation 

All organs require a blood supply from the arteries and 
drainage by veins. Within most organs there are multiple 
ways of perfusing the tissue such that if the main vessel 
feeding the organ or vein draining the organ is blocked, a 
series of smaller vessels (collateral vessels) continue to 
supply and drain the organ. 

In certain circumstances, organs have more than one 
vessel perfusing them, such as the hand, which is supplied 
by the radial and ulnar arteries. Loss of either the radial or 
the ulnar artery may not produce any symptoms of 
reduced perfusion to the hand. 

There are circumstances in which loss of a vein 
produces significant venous collateralization. Some of 
these venous collaterals become susceptible to bleeding. 


This is a considerable problem in patients who have 
undergone portal vein thrombosis or occlusion, where 
venous drainage from the gut bypasses the liver through 
collateral veins to return to the systemic circulation. 

Normal vascular anastomoses associated with an organ 
are important. Some organs, such as the duodenum, have 
a dual blood supply arising from the branches of the 
celiac trunk and also from the branches of the superior 
mesenteric artery. Should either of these vessels be 
damaged, blood supply will be maintained to the organ. 
The brain has multiple vessels supplying it, dominated by 
the carotid arteries and the vertebral arteries. Vessels 
within the brain are end arteries and have a poor 
collateral circulation; hence any occlusion will produce 
long-term cerebral damage. 


28 







Body systems • Lymphatic System 


LYMP HATIC SYSTEM 
Lymphatic vessels 

Lymphatic vessels form an extensive and complex inter¬ 
connected network of channels, which begin as “porous” 
blind-ended lymphatic capillaries in tissues of the body and 
converge to form a number of larger vessels, which ulti¬ 
mately connect with large veins in the root of the neck. 

Lymphatic vessels mainly collect fluid lost from vascular 
capillary beds during nutrient exchange processes and 
deliver it back to the venous side of the vascular system 
(Fig. 1.29). Also included in this interstitial fluid that drains 
into the lymphatic capillaries are pathogens, cells of the 
lymphocytic system, cell products (such as hormones), and 
cell debris. 

In the small intestine, certain fats absorbed and pro¬ 
cessed by the intestinal epithelium are packaged into 
protein-coated lipid droplets (chylomicrons), which are 


released from the epithelial cells and enter the interstitial 
compartment. Together with other components of the 
interstitial fluid, the chylomicrons drain into lymphatic 
capillaries (known as lacteals in the small intestine) and 
are ultimately delivered to the venous system in the neck. 
The lymphatic system is therefore also a major route of 
transport for fat absorbed by the gut. 

The fluid in most lymphatic vessels is clear and colorless 
and is known as lymph. That carried by lymphatic vessels 
from the small intestine is opaque and milky because of the 
presence of chylomicrons and is termed chyle. 

There are lymphatic vessels in most areas of the body 
except the brain, bone marrow, and avascular tissues such 
as epithelia and cartilage. 

The movement of lymph through the lymphatic vessels 
is generated mainly by the indirect action of adjacent 
structures, particularly by contraction of skeletal muscles 
and pulses in arteries. Unidirectional flow is maintained by 
the presence of valves in the vessels. 



Lymphatic capillaries 


Lymph node 


Lymph vessel 
carrying lymph 


Capsule 


Blood vessels 


Capillary bed 


Lymphoid tissue 
(containing lymphocytes 
and 


Fig. 1.29 Lymphatic vessels mainly collect fluid lost from vascular capillary beds during nutrient exchange processes and deliver it back to 
the venous side of the vascular system. 




















































The Body 


Lymph nodes 

Lymph nodes are small (0.1-2.5 cm long) encapsulated 
structures that interrupt the course of lymphatic vessels 
and contain elements of the body’s defense system, such 
as clusters of lymphocytes and macrophages. They act as 
elaborate filters that trap and phagocytose particulate 
matter in the lymph that percolates through them. In addi¬ 
tion, they detect and defend against foreign antigens that 
are also carried in the lymph (Fig. 1.29). 

Because lymph nodes are efficient filters and flow 
through them is slow, cells that metastasize from (migrate 
away from) primary tumors and enter lymphatic vessels 
often lodge and grow as secondary tumors in lymph nodes. 
Lymph nodes that drain regions that are infected or contain 
other forms of disease can enlarge or undergo certain 
physical changes, such as becoming “hard” or “tender.” 
These changes can be used by clinicians to detect patho¬ 
logic changes or to track spread of disease. 

A number of regions in the body are associated with 
clusters or a particular abundance of lymph nodes (Fig. 
1.30). Not surprisingly, nodes in many of these regions 
drain the body’s surface, the digestive system, or the respi¬ 
ratory system. All three of these areas are high-risk sites 
for the entry of foreign pathogens. 

Lymph nodes are abundant and accessible to palpation 
in the axilla, the groin and femoral region, and the neck. 
Deep sites that are not palpable include those associated 
with the trachea and bronchi in the thorax, and with the 
aorta and its branches in the abdomen. 


Lymphatic trunks and ducts 

All lymphatic vessels coalesce to form larger trunks 
or ducts, which drain into the venous system at sites in 
the neck where the internal jugular veins join the 
subclavian veins to form the brachiocephalic veins 
(Fig. 1.31): 

■ Lymph from the right side of the head and neck, the 
right upper limb, right side of the thorax, and right side 
of the upper and more superficial region of the abdomi¬ 
nal wall is carried by lymphatic vessels that connect 
with veins on the right side of the neck. 

■ Lymph from all other regions of the body is carried by 
lymphatic vessels that drain into veins on the lef t side of 
the neck. 

Specific information about the organization of the lym¬ 
phatic system in each region of the body is discussed in the 
appropriate chapter. 


Cervical nodes 

(along course 
of internal 
jugular vein) 

Axillary nodes 

(in axilla) 

Deep nodes 

(related to aorta 
and celiac trunk 
and superior and 
inferior mesenteric 
arteries) 



Pericranial ring 

(base of head) 


Tracheal nodes 

(nodes related to 
trachea and 
bronchi) 


Inguinal nodes 

(along course of 
inguinal ligament) 


Femoral nodes 

(along femoral vein) 


Fig. 1.30 Regions associated with clusters or a particular 
abundance of lymph nodes. 



Fig. 1.31 Major lymphatic vessels that drain into large veins in 
the neck. 



































Body systems • Nervous System 


In the clinic 

Lymph nodes 

Lymph nodes are efficient filters and have an internal 
honeycomb of reticular connective tissue filled with 
lymphocytes. These lymphocytes act on bacteria, viruses, 
and other bodily cells to destroy them. Lymph nodes tend 
to drain specific areas, and if infection occurs within a 
drainage area, the lymph node will become active. The 
rapid cell turnover and production of local inflammatory 
mediators may cause the node to enlarge and become 


tender. Similarly, in patients with malignancy the 
lymphatics may drain metastasizing cells to the lymph 
nodes. These can become enlarged and inflamed and will 
need to be removed if clinically symptomatic. 

Lymph nodes may become diffusely enlarged in certain 
systemic illnesses (e.g., viral infection), or local groups may 
become enlarged with primary lymph node malignancies, 
such as lymphoma (Fig. 1.32). 



Fig. 1.32 A .This computed tomogram with contrast, in the axial plane, demonstrates the normal common carotid arteries and internal 
jugular veins with numerous other nonenhancing nodules that represent lymph nodes in a patient with lymphoma. B. This computed 
tomogram with contrast, in the axial plane, demonstrates a large anterior soft tissue mediastinal mass that represents a lymphoma. 


NERVOUS SYSTEM 

The nervous system can be separated into parts based on 
structure and on function: 

■ structurally, it can be divided into the central nervous 
system (CNS) and the peripheral nervous system (PNS) 
(Fig. 1.33); 

■ functionally, it can be divided into somatic and visceral 
parts. 

The CNS is composed of the brain and spinal cord, both 
of which develop from the neural tube in the embryo. 

The PNS is composed of all nervous structures outside 
the CNS that connect the CNS to the body. Elements of this 


system develop from neural crest cells and as outgrowths 
of the CNS. The PNS consists of the spinal and cranial 
nerves, visceral nerves and plexuses, and the enteric 
system. The detailed anatomy of a typical spinal nerve is 
described in Chapter 2, as is the way spinal nerves are 
numbered. Cranial nerves are described in Chapter 8. 
The details of nerve plexuses are described in chapters 
dealing with the specific regions in which the plexuses are 
located. 

Central nervous system 

Brain 

The parts of the brain are the cerebral hemispheres, the 
cerebellum, and the brainstem. The cerebral hemispheres 






The Body 


Peripheral nervous Central nervous 



consist of an outer portion, or the gray matter, contain¬ 
ing cell bodies; an inner portion, or the white matter, 
made up of axons forming tracts or pathways; and the 
ventricles, which are spaces filled with cerebrospinal 
fluid (CSF). 

The cerebellum has two lateral lobes and a midline 
portion. The components of the brainstem are classically 
defined as the diencephalon, midbrain, pons, and medulla. 
However, in common usage today, the term “brainstem” 
usually refers to the midbrain, pons, and medulla. 

A further discussion of the brain can be found in 
32 Chapter 8. 


Spinal cord 

The spinal cord is the part of the CNS in the superior two 
thirds of the vertebral canal. It is roughly cylindrical in 
shape, and is circular to oval in cross section with a central 
canal. A further discussion of the spinal cord can be found 
in Chapter 2. 

Meninges 

The meninges (Fig. 1.34) are three connective tissue cover¬ 
ings that surround, protect, and suspend the brain and 
spinal cord within the cranial cavity and vertebral canal, 
respectively; 

■ The dura mater is the thickest and most external of the 
coverings. 

■ The arachnoid mater is against the internal surface of 
the dura mater. 

■ The pia mater is adherent to the brain and spinal cord. 

Between the arachnoid and pia mater is the subarach¬ 
noid space, which contains CSF. 

A further discussion of the cranial meninges can 
be found in Chapter 8 and of the spinal meninges in 
Chapter 2 . 


Functional subdivisions of the CNS 

Functionally, the nervous system can be divided into 
somatic and visceral parts. 


Subdural space 
(potential space) 



Subarachnoid space 
Arachnoid mater 
Pia mater 
Cerebral artery/ 


Cerebral cortex ✓ 


Extradural space 
(potential space) 


Diploic vein 


CranialrEndosteal layer 
dura -J 

mater LMeningeal layer 


rExternal 

Skull 

- Internal 


Fig. 1.34 Arrangement of meninges in the cranial cavity. 


































Body systems • Nervous System 


■ The somatic part (soma, from the Greek for “body”) 
innervates structures (skin and most skeletal muscle) 
derived from somites in the embryo, and is mainly 
involved with receiving and responding to information 
from the external environment. 

■ The visceral part ( viscera , from the Greek for “guts”) 
innervates organ systems in the body and other visceral 
elements, such as smooth muscle and glands, in periph¬ 
eral regions of the body. It is concerned mainly with 
detecting and responding to information from the inter¬ 
nal environment. 

Somatic part of the nervous system 

The somatic part of the nervous system consists of: 

■ nerves that carry conscious sensations from peripheral 
regions back to the CNS, and 

■ nerves that innervate voluntary muscles. 


Somatic nerves arise segmentally along the developing 
CNS in association with somites, which are themselves 
arranged segmentally along each side of the neural tube 
(Fig. 1.35). Part of each somite (the dermatomyotome) 
gives rise to skeletal muscle and the dermis of the skin. As 
cells of the dermatomyotome differentiate, they migrate 
into posterior (dorsal) and anterior (ventral) areas of the 
developing body: 

■ Cells that migrate anteriorly give rise to muscles of the 
limbs and trunk (hypaxial muscles) and to the associ¬ 
ated dermis. 

■ Cells that migrate posteriorly give rise to the intrinsic 
muscles of the back (epaxial muscles) and the associ¬ 
ated dermis. 

Developing nerve cells within anterior regions of the 
neural tube extend processes peripherally into posterior 



Body cavity 
(coelom) 


Notochord 


Neural tube 


Somite 


Ectoderm 


Hypaxial muscles and dermis 


Neural crest 


Dermatomyotome 
Lateral plate mesoderm 
Intermediate mesoderm 


Endoderm 


Epaxial muscles and dermis 


Fig. 1.35 Differentiation of somites in a “tubular” embryo. 


33 















The Body 


and anterior regions of the differentiating dermatomyo- 
tome of each somite. 

Simultaneously, derivatives of neural crest cells (cells 
derived from neural folds during formation of the neural 
tube) differentiate into neurons on each side of the neural 
tube and extend processes both medially and laterally 
(Fig. 1.36): 

■ Medial processes pass into the posterior aspect of the 
neural tube. 

■ Lateral processes pass into the differentiating regions of 
the adjacent dermatomyotome. 

Neurons that develop from cells within the spinal cord 
are motor neurons and those that develop from neural 
crest cells are sensory neurons. 

Somatic sensory and somatic motor fibers that are orga¬ 
nized segmentally along the neural tube become parts of 
all spinal nerves and some cranial nerves. 

The clusters of sensory nerve cell bodies derived from 
neural crest cells and located outside the CNS form sensory 
ganglia. 


Generally, all sensory information passes into the poste¬ 
rior aspect of the spinal cord, and all motor fibers leave 
anteriorly. 

Somatic sensory neurons carry information from the 
periphery into the CNS and are also called somatic 
sensory afferents or general somatic afferents 
(GSAs). The modalities carried by these nerves include 
temperature, pain, touch, and proprioception. Propriocep¬ 
tion is the sense of determining the position and movement 
of the musculoskeletal system detected by special receptors 
in muscles and tendons. 

Somatic motor fibers carry information away from the 
CNS to skeletal muscles and are also called somatic motor 
efferents or general somatic efferents (GSEs). Like 
somatic sensory fibers that come from the periphery, somatic 
motor fibers can be very long. They extend from cell bodies 
in the spinal cord to the muscle cells they innervate. 

Dermatomes 

Because cells from a specific somite develop into the dermis 
of the skin in a precise location, somatic sensory fibers 
originally associated with that somite enter the posterior 



Hypaxial muscles 


Somatic sensory neuron 
developing from neural crest cells 


Epaxial (back) muscles 


of neural tube 


Axon of motor neuron 
projects to muscle developing 
from dermatomyotome 


Fig.1.36 Somatic sensory and motor neurons. Blue lines indicate motor nerves and red lines indicate sensory nerves. 










Body systems • Nervous System 


region of the spinal cord at a specific level and become 
part of one specific spinal nerve (Fig. 1.37). Each spinal 
nerve therefore carries somatic sensory information from 
a specific area of skin on the surface of the body. A der¬ 
matome is that area of skin supplied by a single spinal 
cord level, or on one side, by a single spinal nerve. 

There is overlap in the distribution of dermatomes, but 
usually a specific region within each dermatome can be 
identified as an area supplied by a single spinal cord level. 
Testing touch in these autonomous zones in a conscious 
patient can be used to localize lesions to a specific spinal 
nerve or to a specific level in the spinal cord. 


Myotomes 

Somatic motor nerves that were originally associated with 
a specific somite emerge from the anterior region of the 
spinal cord and, together with sensory nerves from the 
same level, become part of one spinal nerve. Therefore 
each spinal nerve carries somatic motor fibers to muscles 
that originally developed from the related somite. A 
myotome is that portion of a skeletal muscle innervated 
by a single spinal cord level or, on one side, by a single 
spinal nerve. 


Somite 



Cranial 


Autonomous region 
(where overlap of 
dermatomes is 
least likely) 
of C6 dermatome 
(pad of thumb) 


Skin on the lateral side of the forearm and on the 
thumb is innervated by C6 spinal level (spinal nerve). 

The dermis of the skin in this region develops from the somite 
initially associated with the C6 level of the developing spinal cord. 


Spinal ganglion 


C6 segment of spinal cord 


Caudal 


Dermatomyotome 


Fig. 137 Dermatomes. 


35 































The Body 


Myotomes are generally more difficult to test than der¬ 
matomes because each skeletal muscle in the body is 
usually innervated by nerves derived from more than one 
spinal cord level (Fig. 1.38). 

Testing movements at successive joints can help in local¬ 
izing lesions to specific nerves or to a specific spinal cord 
level. For example: 


■ Muscles that move the shoulder joint are innervated 
mainly by spinal nerves from spinal cord levels C5 
and C6. 

■ Muscles that move the elbow are innervated mainly by 
spinal nerves from spinal cord levels C6 and C7. 

■ Muscles in the hand are innervated mainly by spinal 
nerves from spinal cord levels C8 and Tl. 


C6 segment of spinal cord 



Dermatomyotome 


C5 segment of spinal cord 


Somite 


Muscles that abduct the arm are innervated 
by C5 and C6 spinal levels (spinal nerves) 
and develop from somites initially associated 
with C5 and C6 regions of developing spinal cord. 


36 


Fig. 1.38 Myotomes. 





















Body systems • Nervous System 


In the clinic 

Dermatomes and myotomes 

A knowledge of dermatomes and myotomes is absolutely 
fundamental to carrying out a neurological examination. A 
typical dermatome map is shown in Fig. 1.39. 

Clinically, a dermatome is that area of skin supplied by 
a single nerve or spinal cord level. A myotome is that 



region of skeletal muscle innervated by a single nerve or 
spinal cord level. Most individual muscles of the body are 
innervated by more than one spinal cord level, so the 
evaluation of myotomes is usually accomplished by 
testing movements of joints or muscle groups. 



Fig. 1.39 Dermatomes. A. Anterior view. B. Posterior view. 








































































The Body 


Visceral part of the nervous system 

The visceral part of the nervous system, as in the somatic 
part, consists of motor and sensory components: 

■ Sensory nerves monitor changes in the viscera. 

■ Motor nerves mainly innervate smooth muscle, cardiac 
muscle, and glands. 

The visceral motor component is commonly referred to 

as the autonomic division of the PNS and is subdivided 
into sympathetic and parasympathetic parts. 


Like the somatic part of the nervous system, the visceral 
part is segmentally arranged and develops in a parallel 
fashion (Fig. 1.40). 

Visceral sensory neurons that arise from neural crest 
cells send processes medially into the adjacent neural tube 
and laterally into regions associated with the developing 
body. These sensory neurons and their processes, referred 
to as general visceral afferent fibers (GVAs), are associ¬ 
ated primarily with chemoreception, mechanoreception, 
and stretch reception. 

Visceral motor neurons that arise from cells in lateral 
regions of the neural tube send processes out of the 


Part of neural crest developing 
Visceral motor ganglion into spinal ganglia 



Visceral sensory neuron develops 
from neural crest and becomes 
part of spinal ganglion 


Visceral motor 
preganglionic 
neuron in lateral 
region of CNS 
(spinal cord) 


Body cavity 
(coelom) 


Motor nerve ending 
associated with 
blood vessels, 
sweat glands, 
arrector pili muscles 
at periphery 


Sensory nerve ending 


Motor nerve ending associated with viscera 


Postganglionic motor neuron is outside CNS. 

An aggregation of postganglionic neuronal cell 
bodies forms a peripheral visceral motor ganglion. 


Developing gastrointestinal tract 


38 


Fig. 1.40 Development of the visceral part of the nervous system. 













Body systems • Nervous System 


anterior aspect of the tube. Unlike in the somatic part, 
these processes, containing general visceral efferent 
fibers (GVEs), synapse with other cells, usually other vis¬ 
ceral motor neurons, that develop outside the CNS from 
neural crest cells that migrate away from their original 
positions close to the developing neural tube. 

The visceral motor neurons located in the spinal cord 
are referred to as preganglionic motor neurons and their 
axons are called preganglionic fibers; the visceral motor 
neurons located outside the CNS are referred to as postgan¬ 
glionic motor neurons and their axons are called postgan¬ 
glionic fibers. 

The cell bodies of the visceral motor neurons outside the 
CNS often associate with each other in a discrete mass 
called a ganglion. 

Visceral sensory and motor fibers enter and leave the 
CNS with their somatic equivalents (Fig. 1.41). Visceral 
sensory fibers enter the spinal cord together with somatic 
sensory fibers through posterior roots of spinal nerves. 
Preganglionic fibers of visceral motor neurons exit the 
spinal cord in the anterior roots of spinal nerves, along 
with fibers from somatic motor neurons. 

Postganglionic fibers traveling to visceral elements in 
the periphery are found in the posterior and anterior rami 
(branches) of spinal nerves. 

Visceral motor and sensory fibers that travel to and from 
viscera form named visceral branches that are separate 
from the somatic branches. These nerves generally form 
plexuses from which arise branches to the viscera. 

Visceral motor and sensory fibers do not enter and leave 
the CNS at all levels (Fig. 1.42): 



Somatic motor and 
visceral motor fibers 

Anterior root (motor) 


— Spinal 
ganglion 

— Spinal 
nerve 

Posterior 

ramus 


Anterior 

ramus 


Somatic sensory and 
visceral sensory fibers 


Posterior root 
(sensory) 


■ In the cranial region, visceral components are associ¬ 
ated with four of the twelve cranial nerves (CN III, VII, 
IX, and X). 

■ In the spinal cord, visceral components are associated 
mainly with spinal cord levels T1 to L2 and S2 to S4. 

Visceral motor components associated with spinal levels 
T1 to L2 are termed sympathetic. Those visceral motor 
components in cranial and sacral regions, on either side of 
the sympathetic region, are termed parasympathetic: 

■ The sympathetic system innervates structures in periph¬ 
eral regions of the body and viscera. 

■ The parasympathetic system is more restricted to inner¬ 
vation of the viscera only. 


Brainstem 
cranial nerves 
III, VII, IX, X 



Parasympathetic 


S2 to S4 
spinal segments 


Sympathetic 

— T1 to L2 
spinal segments 


Fig. 1.41 Basic anatomy of a thoracic spinal nerve. 


Fig. 1.42 Parts of the CNS associated with visceral motor 
components. 


39 

































The Body 


Sympathetic system 

The sympathetic part of the autonomic division of thePNS 
leaves thoracolumbar regions of the spinal cord with 
the somatic components of spinal nerves T1 to L2 (Fig. 
1.43). On each side, a paravertebral sympathetic trunk 
extends from the base of the skull to the inferior end of the 


vertebral column where the two trunks converge anteri¬ 
orly to the coccyx at the ganglion impar. Each trunk is 
attached to the anterior rami of spinal nerves and becomes 
the route by which sympathetics are distributed to the 
periphery and all viscera. 

Visceral motor preganglionic fibers leave the T1 to L2 
part of the spinal cord in anterior roots. The fibers 


Peripheral 


Organs 


Sympathetic nerves follow 
somatic nerves to periphery 
(glands, smooth muscle) 



ffe/-.'. 

%£••••• 

ItcC 

% •• 

•%••• • 

;>• ••. \ 

•*••• • 

•••••_ • 





Ganglion impar 


Pelvic viscera 


Fig. 1.43 Sympathetic part of the autonomic division of the PNS. 































Body systems • Nervous System 


then enter the spinal nerves, pass through the anterior 
rami and into the sympathetic trunks. One trunk is located 
on each side of the vertebral column (paravertebral) and 
positioned anterior to the anterior rami. Along the trunk 
is a series of segmentally arranged ganglia formed from 
collections of postganglionic neuronal cell bodies where 
the preganglionic neurons synapse with postganglionic 
neurons. Anterior rami of T1 to L2 are connected to the 
sympathetic trunk or to a ganglion by a white ramus 
communicans, which carries preganglionic sympathetic 
fibers and appears white because the fibers it contains are 
myelinated. 

Preganglionic sympathetic fibers that enter a paraverte¬ 
bral ganglion or the sympathetic trunk through a white 
ramus communicans may take the following four path¬ 
ways to target tissues: 


1. Peripheral sympathetic innervation at the level 
of origin of the preganglionic fiber 

Preganglionic sympathetic fibers may synapse with post¬ 
ganglionic motor neurons in ganglia associated with the 
sympathetic trunk, after which postganglionic fibers enter 
the same anterior ramus and are distributed with periph¬ 
eral branches of the posterior and anterior rami of that 
spinal nerve (Fig. 1.44). The fibers innervate structures at 
the periphery of the body in regions supplied by the spinal 
nerve. The gray ramus communicans connects the sym¬ 
pathetic trunk or a ganglion to the anterior ramus and 
contains the postganglionic sympathetic fibers. It appears 
gray because postganglionic fibers are nonmyelinated. The 
gray ramus communicans is positioned medial to the white 
ramus communicans. 



T10 spinal nerve 

Posterior 

ramus 


Peripheral distribution of sympathetics 
carried peripherally by terminal cutaneous 
branches of spinal nerve T1 to L2 


Motor nerve to sweat glands, 
smooth muscle of blood 
vessels, and arrector pili 
muscles in the part of T10 
dermatome supplied by the 
anterior ramus 


Anterior 

ramus 


Gray ramus communicans 

White ramus 


Fig. 1.44 Course of sympathetic fibers that travel to the periphery in the same spinal nerves in which they travel out of the spinal cord. 



















The Body 



cord. 


2. Peripheral sympathetic innervation above or 
below the level of origin of the preganglionic fiber 

Preganglionic sympathetic fibers may ascend or descend to 
other vertebral levels where they synapse in ganglia associ¬ 
ated with spinal nerves that may or may not have visceral 
motor input directly from the spinal cord (i.e., those nerves 
other than T1 to L2) (Fig. 1.45). 

The postganglionic fibers leave the distant ganglia via 
gray rami communicantes and are distributed along the 
posterior and anterior rami of the spinal nerves. 

The ascending and descending fibers, together with all 
the ganglia, form the paravertebral sympathetic trunk, 
which extends the entire length of the vertebral column. 
The formation of this trunk, on each side, enables visceral 
42 motor fibers of the sympathetic part of the autonomic 


division of the PNS, which ultimately emerge from only a 
small region of the spinal cord (T1 to L2), to be distributed 
to peripheral regions innervated by all spinal nerves. 

White rami communicantes only occur in association 
with spinal nerves T1 to L2, whereas gray rami communi¬ 
cantes are associated with all spinal nerves. 

Fibers from spinal cord levels T1 to T5 pass predomi¬ 
nantly superiorly, whereas fibers from T5 to L2 pass interi¬ 
orly. All sympathetics passing into the head have 
preganglionic fibers that emerge from spinal cord level 
T1 and ascend in the sympathetic trunks to the highest 
ganglion in the neck (the superior cervical ganglion), 
where they synapse. Postganglionic fibers then travel along 
blood vessels to target tissues in the head, including blood 
vessels, sweat glands, small smooth muscles associated 
with the upper eyelids, and the dilator of the pupil. 








































Body systems • Nervous System 


3. Sympathetic innervation of thoracic 
and cervical viscera 

Preganglionic sympathetic fibers may synapse with post¬ 
ganglionic motor neurons in ganglia and then leave the 
ganglia medially to innervate thoracic or cervical viscera 
(Fig. 1.46). They may ascend in the trunk before synaps- 
ing, and after synapsing the postganglionic fibers may 


combine with those from other levels to form named vis¬ 
ceral nerves, such as cardiac nerves. Often, these nerves 
join branches from the parasympathetic system to form 
plexuses on or near the surface of the target organ, for 
example, the cardiac and pulmonary plexuses. Branches 
of the plexus innervate the organ. Spinal cord levels T1 
to T5 mainly innervate cranial, cervical, and thoracic 
viscera. 



Fig. 1.46 Course of sympathetic nerves traveling to the heart 



























The Body 


4. Sympathetic innervation of the abdomen and pelvic 
regions and the adrenals 

Preganglionic sympathetic fibers may pass through the 
sympathetic trunk and paravertebral ganglia without syn- 
apsing and, together with similar fibers from other levels, 
form splanchnic nerves (greater, lesser, least, lumbar, 


and sacral), which pass into the abdomen and pelvic 
regions (Fig. 1.47). The preganglionic fibers in these 
nerves are derived from spinal cord levels T5 to L2. 

The splanchnic nerves generally connect with sympa¬ 
thetic ganglia around the roots of major arteries that 
branch from the abdominal aorta. These ganglia are part 
of a large prevertebral plexus that also has input from the 



White ramus 
communicans 

Gray ramus 
communicans 


Greater splanchnic nerves 


Lesser splanchnic nerves 


Least splanchnic nerves 


Lumbar splanchnic nerves 


Prevertebral plexus 
and ganglia 


- Paravertebral - 
sympathetic trunk 


Abdominal 

and 


Sacral splanchnic nerves 


44 


Fig. 1.47 Course of sympathetic nerves traveling to abdominal and pelvic viscera. 



























































Body systems • Nervous System 


parasympathetic part of the autonomic division of the 
PNS. Postganglionic sympathetic fibers are distributed in 
extensions of this plexus, predominantly along arteries, to 
viscera in the abdomen and pelvis. 

Some of the preganglionic fibers in the prevertebral 
plexus do not synapse in the sympathetic ganglia of the 
plexus but pass through the system to the adrenal gland, 
where they synapse directly with cells of the adrenal 


medulla. These cells are homologues of sympathetic post¬ 
ganglionic neurons and secrete adrenaline and noradrena¬ 
line into the vascular system. 

Parasympathetic system 

The parasympathetic part of the autonomic division of the 
PNS (Fig. 1.48) leaves cranial and sacral regions of the 
CNS in association with: 



Cranial parasympathetic 
outflow via cranial nerves 


[III] 


[VII] 


[X] 



Ciliary ganglion 



Pterygopalatine 

ganglion 

Otic ganglion 


Submandibular 

ganglion 



Lacrimal gland 
Pupillary constriction 
Parotid gland 


Salivary glands 



S2 to S4 


Sacral parasympathetic 
outflow via pelvic 
splanchnic nerves 



A 


v 





Transition from supply by [X] 
to pelvic splanchnic nerves 


Erectile tissues of penis 
and clitoris 


Abdominal viscera 


-Synapse with nerve cells 

of enteric system 


Pelvic viscera 


Fig. 1.48 Parasympathetic part of the autonomic division of the PNS. 



























































The Body 


■ cranial nerves III, VII, IX, and X: III, VII, and IX 
carry parasympathetic fibers to structures within 
the head and neck only, whereas X (the vagus 
nerve) also innervates thoracic and most abdominal 
viscera; and 

■ spinal nerves S2 to S4: sacral parasympathetic fibers 
innervate inferior abdominal viscera, pelvic viscera, and 
the arteries associated with erectile tissues of the 
perineum. 

Like the visceral motor nerves of the sympathetic part, 
the visceral motor nerves of the parasympathetic part gen¬ 
erally have two neurons in the pathway. The preganglionic 
neurons are in the CNS, and fibers leave in the cranial 
nerves. 

Sacral preganglionic parasympathetic fibers 

In the sacral region, the preganglionic parasympathetic 
fibers form special visceral nerves (the pelvic splanchnic 
nerves), which originate from the anterior rami of S2 to 
S4 and enter pelvic extensions of the large prevertebral 
plexus formed around the abdominal aorta. These fibers 
are distributed to pelvic and abdominal viscera mainly 
along blood vessels. The postganglionic motor neurons are 
in the walls of the viscera. In organs of the gastrointestinal 
system, preganglionic fibers do not have a postganglionic 
parasympathetic motor neuron in the pathway; instead, 
preganglionic fibers synapse directly on neurons in the 
ganglia of the enteric system. 

Cranial nerve preganglionic 
parasympathetic fibers 

The preganglionic parasympathetic motor fibers in CN 
III, VII, and IX separate from the nerves and connect 
with one of four distinct ganglia, which house postgangli¬ 
onic motor neurons. These four ganglia are near major 
branches of CN V. Postganglionic fibers leave the ganglia, 
join the branches of CN V, and are carried to target tissues 
(salivary, mucous, and lacrimal glands; constrictor muscle 
of the pupil; and ciliary muscle in the eye) with these 
branches. 


The vagus nerve [X] gives rise to visceral branches along 
its course. These branches contribute to plexuses associ¬ 
ated with thoracic viscera or to the large prevertebral 
plexus in the abdomen and pelvis. Many of these plexuses 
also contain sympathetic fibers. 

When present, postganglionic parasympathetic neurons 
are in the walls of the target viscera. 

Visceral sensory innervation (visceral afferents) 

Visceral sensory fibers generally accompany visceral 
motor fibers. 

Visceral sensory fibers accompany 
sympathetic fibers 

Visceral sensory fibers follow the course of sympathetic 
fibers entering the spinal cord at similar spinal cord levels. 
However, visceral sensory fibers may also enter the spinal 
cord at levels other than those associated with motor 
output. For example, visceral sensory fibers from the heart 
may enter at levels higher than spinal cord level Tl. Vis¬ 
ceral sensory fibers that accompany sympathetic fibers are 
mainly concerned with detecting pain. 

Visceral sensory fibers accompany 
parasympathetic fibers 

Visceral sensory fibers accompanying parasympathetic 
fibers are carried mainly in IX and X and in spinal nerves 
S2 to S4. 

Visceral sensory fibers in IX carry information from che- 
moreceptors and baroreceptors associated with the walls 
of major arteries in the neck, and from receptors in the 
pharynx. 

Visceral sensory fibers in X include those from cervical 
viscera, and major vessels and viscera in the thorax and 
abdomen. 

Visceral sensory fibers from pelvic viscera and the distal 
parts of the colon are carried in S2 to S4. 

Visceral sensory fibers associated with parasympathetic 
fibers primarily relay information to the CNS about the 
status of normal physiological processes and reflex 
activities. 



Body systems • Nervous System 



Peritoneum 


Mesentery 


Circular muscle layer 


Submucosa muscle 


Myenteric plexus 


— Enteric nervous system 


Preganglionic 

sympathetic 

Postganglionic 

sympathetic 

Preganglionic 

parasympathetic 

Visceral afferent 


Vagal afferent 


P re vertebral 
sympathetic ganglion 

Blood vessel 


Longitudinal muscle layer 


Submucous plexus 


Submucosa 


Fig. 1.49 Enteric part of the nervous system. 


The enteric system 

The enteric nervous system consists of motor and sensory 
neurons and their support cells, which form two intercon¬ 
nected plexuses, the myenteric and submucous nerve 
plexuses, within the walls of the gastrointestinal tract 
(Fig. 1.49). Each of these plexuses is formed by: 

■ ganglia, which house the nerve cell bodies and associ¬ 
ated cells, and 


■ bundles of nerve fibers, which pass between ganglia and 
from the ganglia into surrounding tissues. 

Neurons in the enteric system are derived from neural 
crest cells originally associated with occipitocervical and 
sacral regions. Interestingly, more neurons are reported to 
be in the enteric system than in the spinal cord itself. 

Sensory and motor neurons within the enteric system 
control reflex activity within and between parts of the 




































The Body 


gastrointestinal system. These reflexes regulate peristalsis, 
secretomotor activity, and vascular tone. These activities 
can occur independently of the brain and spinal cord, but 
can also be modified by input from preganglionic parasym¬ 
pathetic and postganglionic sympathetic fibers. 

Sensory information from the enteric system is carried 
back to the CNS by visceral sensory fibers. 

Nerve plexuses 

Nerve plexuses are either somatic or visceral and combine 
fibers from different sources or levels to form new nerves 
with specific targets or destinations (Fig. 1.50). Plexuses of 
the enteric system also generate reflex activity independent 
of the CNS. 

Somatic plexuses 

Major somatic plexuses formed from the anterior rami of 
spinal nerves are the cervical (Cl to C4), brachial (C5 to 
Tl), lumbar (LI to L4), sacral (L4 to S4), and coccygeal (S5 
to Co) plexuses. Except for spinal nerve Tl, the anterior 
rami of thoracic spinal nerves remain independent and do 
not participate in plexuses. 

Visceral plexuses 

Visceral nerve plexuses are formed in association with 
viscera and generally contain efferent (sympathetic and 
parasympathetic) and afferent components (Fig. 1.50). 
These plexuses include cardiac and pulmonary plexuses in 
the thorax and a large prevertebral plexus in the abdomen 
anterior to the aorta, which extends interiorly onto the 
lateral walls of the pelvis. The massive prevertebral plexus 
supplies input to and receives output from all abdominal 
and pelvic viscera. 


In the clinic 

Referred pain 

Referred pain occurs when sensory information comes 
to the spinal cord from one location but is interpreted 
by the CNS as coming from another location innervated 
by the same spinal cord level. Usually, this happens 
when the pain information comes from a region, such 
as the gut, which has a low amount of sensory output. 
These afferents converge on neurons at the same spinal 
cord level that receive information from the skin, which 
is an area with a high amount of sensory output. As a 
result, pain from the normally low output region is 
interpreted as coming from the normally high 
output region. 

Pain is most often referred from a region innervated 
by the visceral part of the nervous system to a region 
innervated, at the same spinal cord level, by the somatic 
side of the nervous system. 

Pain can also be referred from one somatic region 
to another. For example, irritation of the peritoneum 
on the inferior surface of the diaphragm, which is 
innervated by the phrenic nerve, can be referred to 
the skin on the top of the shoulder, which is innervated 
by other somatic nerves arising at the same spinal 
cord level. 


OTHER SYSTEMS 

Specific information about the organization and compo¬ 
nents of the respiratory, gastrointestinal, and urogenital 
systems will be discussed in each of the succeeding chap¬ 
ters of this text. 


48 



Body systems • Other Systems 


SOMATIC PLEXUSES 


VISCERAL PLEXUSES 



Prevertebral plexus 


Cervical plexus 

anterior rami Cl to C4 


Brachial plexus 

anterior rami C5 to T1 


Splanchnic 

nerves 


Lumbar plexus 

anterior rami LI to L4 


Sacral plexus 

anterior rami 
L4 to S4 


Sacral splanchnic nerves 


S2 to S4 pelvic splanchnic nerves 
(parasympathetic) 


Parasympathetic [X] 


Cardiac branches 

Pulmonary branch 

Cardiac plexus 

Pulmonary branches 

Esophageal plexus 
Thoracic aortic plexus 

Vagal trunk 


Ganglion impar 


Fig. 1.50 Nerve plexuses. 









































































(f if The Body 


Clinical cases 


Case 1 


APPENDICITIS 

A young man sought medical care because of central 
abdominal pain that was diffuse and colicky. After 
some hours, the pain began to localize in the right 
iliac fossa and became constant. He was referred to an 
abdominal surgeon, who removed a grossly inflamed 
appendix. The patient made an uneventful recovery. 

When the appendix becomes inflamed, the visceral 
sensory fibers are stimulated. These fibers enter the 
spinal cord with the sympathetic fibers at spinal cord 
level T10. The pain is referred to the dermatome of T10, 
which is in the umbilical region (Fig. 1.51). The pain is 
diffuse, not focal; every time a peristaltic wave passes 
through the ileocecal region, the pain recurs. This 
intermittent type of pain is referred to as colic. 

In the later stages of the disease, the appendix contacts 
and irritates the parietal peritoneum in the right iliac 
fossa, which is innervated by somatic sensory nerves. This 
produces a constant focal pain, which predominates over 
the colicky pain that the patient felt some hours 
previously. The patient no longer interprets the referred 
pain from the T10 dermatome. 

Although this is a typical history for appendicitis, it 
should always be borne in mind that the patient's 
symptoms and signs may vary. The appendix is situated 
in a retrocecal position in approximately 70% of patients; 
therefore it may never contact the parietal peritoneum 
anteriorly in the right iliac fossa. It is also possible that 
the appendix is long and may directly contact other 
structures. As a consequence, the patient may have other 
symptoms (e.g., the appendix may contact the ureter, 
and the patient may then develop urological symptoms). 

Although appendicitis is common, other disorders, for 
example of the bowel and pelvis, may produce similar 
symptoms. 



Fig. 1.51 Mechanism for referred pain from an inflamed 
appendix to the T10 dermatome. 


50 












for Chapter 2, Back, 
on STUDENT CONSULT 

( )• 


Image Library—illustrations of back anatomy, 
Chapter 2 

Self-Assessment—National Board style multiple- 
choice questions, Chapter 2 
Short Questions—these are questions requiring 
short responses, Chapter 2 
Interactive Surface Anatomy—interactive surface 
animations, Chapter 2 
■ PT Case Studies, Chapter 2 
Low back instability 
Stenosis 

Herniated nucleus pulposus 

Atlanto-occipital dysfunction 

Atlanto-axial dysfunction 

Mid-cervical dysfunction 

Cauda equina syndrome 

Cervical degenerative joint disease 

Cervical radiculopathy 

Medical Clinical Case Studies, Chapter 2 

Ankylosing spondylitis 

Atlas fracture 

Cervical facet syndrome 

Lumbar puncture 

Spinal cord infarction 

FREE Online Anatomy and Embryology 
Self-Study Course 

Anatomy modules 23 through 25 



General description 
Functions 
Support 
Movement 

Protection of the nervous system 

Component parts 
Bones 

Muscles Tf/7 H u 
Vertebral canal 
Spinal nerves 

Relationship to other regions 
Head 

Thorax, abdomen, and pelvis 
Limbs 

Key features 

Long vertebral column and short spinal cord 
Intervertebral foramina and spinal nerves 
Innervation of the back 

Regional anatomy 

Skeletal framework 
Vertebrae 

Intervertebral foramina 

Posterior spaces between vertebral arches 

Joints 

Joints between vertebrae in the back 

Ligaments 

Anterior and posterior longitudinal ligaments 
Ligamenta flava 

Supraspinous ligament and ligamentum 
nuchae 

Interspinous ligaments 
Back musculature 

Superficial group of back muscles 
Intermediate group of back muscles 
Deep group of back muscles 
Suboccipital muscles 




Spinal cord 99 

Vasculature 100 
Meninges 103 

Arrangement of structures in the vertebral 
canal 104 
Spinal nerves 106 

Surface anatomy 111 

Back surface anatomy 111 
Absence of lateral curvatures 111 


Primary and secondary curvatures in the sagittal 
plane 112 

Useful nonvertebral skeletal landmarks 112 
How to identify specific vertebral spinous 
processes 114 

Visualizing the inferior ends of the spinal cord and 
subarachnoid space 115 
Identifying major muscles 116 

Clinical cases 118 



Conceptual overview • General Description 


2 


Conceptual overview 

GENERAL DESCRIPTION 


The back consists of the posterior aspect of the body and 
provides the musculoskeletal axis of support for the trunk. 
Bony elements consist mainly of the vertebrae, although 
proximal elements of the ribs, superior aspects of the pelvic 
bones, and posterior basal regions of the skull contribute 
to the back’s skeletal framework (Fig. 2.1). 


Associated muscles interconnect the vertebrae and ribs 
with each other and with the pelvis and skull. The back 
contains the spinal cord and proximal parts of the spinal 
nerves, which send and receive information to and from 
most of the body. 


Vertebral column 



bone 


Fig. 2.1 Skeletal framework of the back. 


53 


























Back 


FUNCTIONS 

Support 

The skeletal and muscular elements of the back 
support the body’s weight, transmit forces through the 
pelvis to the lower limbs, carry and position the head, 
and brace and help maneuver the upper limbs. The verte¬ 
bral column is positioned posteriorly in the body at the 
midline. When viewed laterally, it has a number of curva¬ 
tures (Fig. 2.2): 

■ The primary curvature of the vertebral column is 
concave anteriorly, reflecting the original shape of the 
embryo, and is retained in the thoracic and sacral 
regions in adults. 

■ Secondary curvatures, which are concave posteriorly, 
form in the cervical and lumbar regions and bring the 
center of gravity into a vertical line, which allows the 
body’s weight to be balanced on the vertebral column in 
away that expends the least amount of muscular energy 
to maintain an upright bipedal stance. 

As stresses on the back increase from the cervical to 
lumbar regions, lower back problems are common. 


Movement 

Muscles of the back consist of extrinsic and intrinsic 
groups: 

■ The extrinsic muscles of the back move the upper limbs 
and the ribs. 

■ The intrinsic muscles of the back maintain posture and 
move the vertebral column; these movements include 
flexion (anterior bending), extension, lateral flexion, 
and rotation (Fig. 2.3). 

Although the amount of movement between any two 
vertebrae is limited, the effects between vertebrae are addi¬ 
tive along the length of the vertebral column. Also, freedom 
of movement and extension are limited in the thoracic 
region relative to the lumbar part of the vertebral column. 
Muscles in more anterior regions flex the vertebral column. 


Early embryo 



Adult 


Cervical curvature 
(secondary curvature) 


Thoracic curvature 
(primary curvature) 


Lumbar curvature 
(secondary curvature) 

Sacral/coccygeal curvature 
(primary curvature) 


Gravity line 


Fig. 2.2 Curvatures of the vertebral column. 

















Conceptual overview • Functions 


2 



In the cervical region, the first two vertebrae and associ¬ 
ated muscles are specifically modified to support and posi¬ 
tion the head. The head flexes and extends, in the nodding 
motion, on vertebra Cl, and rotation of the head occurs as 
vertebra Cl moves on vertebra CII (Fig. 2.3). 

Protection of the nervous system 

The vertebral column and associated soft tissues of the 
back contain the spinal cord and proximal parts of the 
spinal nerves (Fig. 2.4). The more distal parts of the spinal 
nerves pass into all other regions of the body, including 
certain regions of the head. 


Fig. 2.4 Nervous system. 



55 















































Back 


COMPONENT PARTS 
Bones 

The major bones of the back are the 33 vertebrae (Fig. 
2.5). The number and specific characteristics of the verte¬ 
brae vary depending on the body region with which they 


are associated. There are seven cervical, twelve thoracic, 
five lumbar, five sacral, and three to four coccygeal verte¬ 
brae. The sacral vertebrae fuse into a single bony element, 
the sacrum. The coccygeal vertebrae are rudimentary in 
structure, vary in number from three to four, and often fuse 
into a single coccyx. 



7 cervical vertebrae (CI-CVII) 


12 thoracic vertebrae (TI-TXII) 


5 lumbar vertebrae (LI-LV) 


Sacrum 

(5 fused sacral vertebrae l-V) 
Coccyx 

(3-4 fused coccygeal vertebrae l-IV) 


Fig. 2.5 Vertebrae. 


































Conceptual overview • Component Ports 


2 


Typical vertebra 

A typical vertebra consists of a vertebral body and a verte¬ 
bral arch (Fig. 2.6). 

The vertebral body is anterior and is the major weight¬ 
bearing component of the bone. It increases in size 
from vertebra CII to vertebra LV. Fibrocartilaginous inter¬ 
vertebral discs separate the vertebral bodies of adjacent 
vertebrae. 

The vertebral arch is firmly anchored to the posterior 
surface of the vertebral body by two pedicles, which form 
the lateral pillars of the vertebral arch. The roof of the 
vertebral arch is formed by right and left laminae, which 
fuse at the midline. 

The vertebral arches of the vertebrae are aligned to 
form the lateral and posterior walls of the vertebral canal, 
which extends from the first cervical vertebra (Cl) to the 
last sacral vertebra (vertebra SV). This bony canal contains 
the spinal cord and its protective membranes, together 
with blood vessels, connective tissue, fat, and proximal 
parts of spinal nerves. 

The vertebral arch of a typical vertebra has a number 
of characteristic projections, which serve as: 

■ attachments for muscles and ligaments, 

■ levers for the action of muscles, and 

■ sites of articulation with adjacent vertebrae. 

A spinous process projects posteriorly and generally 
interiorly from the roof of the vertebral arch. 


On each side of the vertebral arch, a transverse process 
extends laterally from the region where a lamina meets a 
pedicle. From the same region, a superior articular process 
and an inferior articular process articulate with similar 
processes on adjacent vertebrae. 

Each vertebra also contains rib elements. In the thorax, 
these costal elements are large and form ribs, which articu¬ 
late with the vertebral bodies and transverse processes. 
In all other regions, these rib elements are small and are 
incorporated into the transverse processes. Occasionally, 
they develop into ribs in regions other than the thorax, 
usually in the lower cervical and upper lumbar regions. 

Muscles 

Muscles in the back can be classified as extrinsic or intrinsic 
based on their embryological origin and type of innerva¬ 
tion (Fig. 2.7). 

The extrinsic muscles are involved with movements of 
the upper limbs and thoracic wall and, in general, are 
innervated by anterior rami of spinal nerves. The superfi¬ 
cial group of these muscles is related to the upper limbs, 
while the intermediate layer of muscles is associated with 
the thoracic wall. 

All of the intrinsic muscles of the back are deep in 
position and are innervated by the posterior rami of 
spinal nerves. They support and move the vertebral 
column and participate in moving the head. One group 
of intrinsic muscles also moves the ribs relative to the ver¬ 
tebral column. 



Fig. 2.6 A typical vertebra. A. Superior view. B. Lateral view. 


57 

























Back 



Trapezius 


Latissimus 

dorsi 


Rhomboid major 


Serratus posterior 
inferior 


Levator scapulae 


Rhomboid minor 


Superficial group 



Intermediate group 


L Extrinsic muscles 

Innervated by anterior rami of spinal nerves or cranial nerve XI (trapezius) 



i 


Intrinsic muscles 

B True back muscles innervated by posterior rami of spinal nerves 

Fig. 2.7 Back muscles. A. Extrinsic muscles. B. Intrinsic muscles. 



























Conceptual overview • Component Ports 


2 


Vertebral canal 

The spinal cord lies within a bony canal formed by adjacent 
vertebrae and soft tissue elements (the vertebral canal) 
(Fig. 2.8): 

■ The anterior wall is formed by the vertebral bodies 
of the vertebrae, intervertebral discs, and associated 
ligaments. 

■ The lateral walls and roof are formed by the vertebral 
arches and ligaments. 

Within the vertebral canal, the spinal cord is surrounded 
by a series of three connective tissue membranes (the 
meninges): 


■ The pia mater is the innermost membrane and is 
intimately associated with the surface of the 
spinal cord. 

■ The second membrane, the arachnoid mater, is sepa¬ 
rated from the pia by the subarachnoid space, which 
contains cerebrospinal fluid. 

■ The thickest and most external of the membranes, the 
dura mater, lies directly against, but is not attached to, 
the arachnoid mater. 

In the vertebral canal, the dura mater is separated 
from surrounding bone by an extradural (epidural) space 
containing loose connective tissue, fat, and a venous 
plexus. 



Anterior internal vertebral 
venous plexus 


Posterior longitudinal 
ligament 


Extradural space 
Extradural fat 

Vertebral body 


Intervertebral disc 


Spinal cord 
Pia mater 

Subarachnoid space 
Arachnoid mater 
Dura mater 


Position of spinal ganglion 


Posterior ramus 


Anterior ramus 


Transverse 

process 


Spinous 

process 


Fig. 2.8 Vertebral canal. 


59 

















Back 


Spinal nerves 

The 31 pairs of spinal nerves are segmental in distribution 
and emerge from the vertebral canal between the pedicles 
of adjacent vertebrae. There are eight pairs of cervical 
nerves (Cl to C8), twelve thoracic (T1 to T12), five lumbar 
(LI to L5), five sacral (SI to S5), and one coccygeal (Co). 
Each nerve is attached to the spinal cord by a posterior root 
and an anterior root (Fig. 2.9). 

After exiting the vertebral canal, each spinal nerve 
branches into: 


■ a posterior ramus—collectively, the small posterior rami 
innervate the back; and 

■ an anterior ramus—the much larger anterior rami 
innervate most other regions of the body except the 
head, which is innervated predominantly, but not exclu¬ 
sively, by cranial nerves. 

The anterior rami form the major somatic plexuses (cer¬ 
vical, brachial, lumbar, and sacral) of the body. Major vis¬ 
ceral components of the PNS (sympathetic trunk and 
prevertebral plexus) of the body are also associated mainly 
with the anterior rami of spinal nerves. 



\ \\ 


- Prevertebral plexus 


Vertebral body 

Anterior root 


.1 components 


Posterior root 


Spinal cord 


Pia mater 


Spinous process 


Lamina 


Sympathetic ganglion 

Anterior ramus 


Posterior ramus 


Spinal nerve 


Extradural space 


Arachnoid mater 
Dura mater 
Subarachnoid space 


Aorta 


Prevertebral ganglion 
(sympathetic) 


Fig. 2.9 Spinal nerves (transverse section). 
















Conceptual overview • Relationship to Other Regions 


2 


RELATIONSHIP TO OTHER REGIONS 
Head 

Cervical regions of the back constitute the skeletal and 
much of the muscular framework of the neck, which in 
turn supports and moves the head (Fig. 2.10). 


The brain and cranial meninges are continuous with 
the spinal cord meninges at the foramen magnum of the 
skull. The paired vertebral arteries ascend, one on each 
side, through foramina in the transverse processes of cervi¬ 
cal vertebrae and pass through the foramen magnum to 
participate, with the internal carotid arteries, in supplying 
blood to the brain. 



Fig. 2.10 Relationships of the back to other regions. 


61 






















Subarachnoid 

space 



62 


Back 


Thorax, abdomen, and pelvis 

The different regions of the vertebral column contribute to 
the skeletal framework of the thorax, abdomen, and pelvis 
(Fig. 2.10). In addition to providing support for each of 
these parts of the body, the vertebrae provide attachments 
for muscles and fascia, and articulation sites for other 
bones. The anterior rami of spinal nerves associated with 
the thorax, abdomen, and pelvis pass into these parts of 
the body from the back. 


Limbs 

The bones of the back provide extensive attachments for 
muscles associated with anchoring and moving the upper 
limbs on the trunk. This is less true of the lower limbs, 
which are firmly anchored to the vertebral column through 
articulation of the pelvic bones with the sacrum. The 
upper and lower limbs are innervated by anterior rami of 
spinal nerves that emerge from cervical and lumbosacral 
levels, respectively, of the vertebral column. 


KEY FEATURES 

Long vertebral column and short 
spinal cord 

During development, the vertebral column grows much 
faster than the spinal cord. As a result, the spinal cord 
does not extend the entire length of the vertebral canal 
(Fig. 2.11). 

In the adult, the spinal cord typically ends between ver¬ 
tebrae LI and LII, although it can end as high as vertebra 
TXII and as low as the disc between vertebrae LII and LIII. 

Spinal nerves originate from the spinal cord at increas¬ 
ingly oblique angles from vertebrae Cl to Co, and the nerve 
roots pass in the vertebral canal for increasingly longer 
distances. Their spinal cord level of origin therefore 
becomes increasingly dissociated from their vertebral 
column level of exit. This is particularly evident for lumbar 
and sacral spinal nerves. 


Cervical 
enlargement 
(of spinal cord) 


Pedicles of 
vertebrae 


Spinal 

ganglion 


Lumbosacral 
enlargement 
(of spinal cord) 

End of spinal 
cord at LI-LI I 
vertebrae 


Arachnoid mater 
Dura mater 


End of 
subarachnoid 
space-sacral 
vertebra II 



Fig. 2.11 Vertebral canal, spinal cord, and spinal nerves. 


Co 

































































Conceptual overview • Key Features 


2 


Intervertebral foramina and spinal nerves 

Each spinal nerve exits the vertebral canal laterally through 
an intervertebral foramen (Fig. 2.12). The foramen is 
formed between adjacent vertebral arches and is closely 
related to intervertebral joints: 

■ The superior and inferior margins are formed by notches 
in adjacent pedicles. 

■ The posterior margin is formed by the articular pro¬ 
cesses of the vertebral arches and the associated joint. 

■ The anterior border is formed by the intervertebral 
disc between the vertebral bodies of the adjacent 
vertebrae. 


Any pathology that occludes or reduces the size of an 
intervertebral foramen, such as bone loss, herniation of 
the intervertebral disc, or dislocation of the zygapophysial 
joint (the joint between the articular processes), can affect 
the function of the associated spinal nerve. 

Innervation of the back 

Posterior branches of spinal nerves innervate the intrinsic 
muscles of the back and adjacent skin. The cutaneous dis¬ 
tribution of these posterior rami extends into the gluteal 
region of the lower limb and the posterior aspect of the 
head. Parts of dermatomes innervated by the posterior 
rami of spinal nerves are shown in Fig. 2.13. 



Superior articular process 


Joint between 
superior and inferior 
articular processes 
(zygapophysial joint) 


Superior vertebral notch 

Intervertebral 
foramen 

Spinal 
nerve 


Intervertebral 

disc 


Inferior articular process Inferior vertebral notch 
Fig. 2.12 Intervertebral foramina. 



*The dorsal rami of L4 and L5 may not have cutaneous 
branches and may therefore not be represented as 
dermatomes on the back 

Fig. 2.13 Dermatomes innervated by posterior rami of spinal 
nerves. 


63 
























Back 


Regional anatomy 

SKELETAL FRAMEWORK 

Skeletal components of the back consist mainly of the ver¬ 
tebrae and associated intervertebral discs. The skull, scap¬ 
ulae, pelvic bones, and ribs also contribute to the bony 
framework of the back and provide sites for muscle 
attachment. 


Vertebrae 

There are approximately 33 vertebrae, which are subdi¬ 
vided into five groups based on morphology and location 
(Fig. 2.14): 

■ The seven cervical vertebrae between the thorax and 
skull are characterized mainly by their small size and 
the presence of a foramen in each transverse process 
(Figs. 2.14 and 2.15). 




Anterior 


7 Cervical 
vertebrae 


Fused costal 
(rib) element 


Foramen 

transversarium 


Cervical vertebra 


Lumbar vertebra 


Thoracic vertebra 


Fused costal 
(rib) element 


■ 5 Lumbar 
vertebrae 


Posterior 


Fig. 2.14 Vertebrae. 

































Regional anatomy • Skeletal Framework 


2 


-Cll 



Vertebral Posterior tubercle 

body of Clll - ] of Cl (atlas) 



Location of_| Vertebra prominens_ 

intervertebral disc (spinous process of CVII) 


Fig. 2.15 Radiograph of cervical region of vertebral column. A. Anteroposterior view. B. Lateral view. 


65 




Back 


The 12 thoracic vertebrae are characterized by their 
articulated ribs (Figs. 2.14 and 2.16); although all ver¬ 
tebrae have rib elements, these elements are small and 
are incorporated into the transverse processes in regions 
other than the thorax; but in the thorax, the ribs are 
separate bones and articulate via synovial joints with 
the vertebral bodies and transverse processes of the 
associated vertebrae. 

Inferior to the thoracic vertebrae are five lumbar verte¬ 
brae, which form the skeletal support for the posterior 
abdominal wall and are characterized by their large size 
(Figs. 2.14 and 2.17). 


■ Next are five sacral vertebrae fused into one single bone 
called the sacrum, which articulates on each side with 
a pelvic bone and is a component of the pelvic wall. 

■ Inferior to the sacrum is a variable number, usually four, 
of coccygeal vertebrae, which fuse into a single small 
triangular bone called the coccyx. 

In the embryo, the vertebrae are formed intersegmen- 
tally from cells called sclerotomes, which originate from 
adjacent somites (Fig. 2.18). Each vertebra is derived from 
the cranial parts of the two somites below, one on each 
side, and the caudal parts of the two somites above. The 



Fig. 2.16 Radiograph of thoracic region of vertebral column. A. Anteroposterior view. B. Lateral view. 







Regional anatomy • Skeletal Framework 


2 


Location of_ 
intervertebral ( 



Intervertebral foramen — 

Spinous process of LI V —' '— Pedicle Vertebral body of LI 11 - 

Fig. 2.17 Radiograph of lumbar region of vertebral column. A. Anteroposterior view. B. Lateral view. 



Somites 


Neural tube 

Cranial 
Forming vertebra 
Migrating sclerotome cells- 


Sclerotome 


Developing 
nerve 


Somites 


Caudal 


Fig. 2.18 Development of the vertebrae. 


67 













Back 


spinal nerves develop segmentally and pass between the 
forming vertebrae. 

Typical vertebra 

A typical vertebra consists of a vertebral body and a poste¬ 
rior vertebral arch (Fig. 2.19). Extending from the verte¬ 
bral arch are a number of processes for muscle attachment 
and articulation with adjacent bone. 

The vertebral body is the weight-bearing part of the 
vertebra and is linked to adjacent vertebral bodies by inter¬ 
vertebral discs and ligaments. The size of vertebral bodies 
increases inferiorly as the amount of weight supported 
increases. 

The vertebral arch forms the lateral and posterior 
parts of the vertebral foramen. 

The vertebral foramina of all the vertebrae together 
form the vertebral canal, which contains and protects 
the spinal cord. Superiorly, the vertebral canal is continu¬ 
ous, through the foramen magnum of the skull, with the 
cranial cavity of the head. 



The vertebral arch of each vertebra consists of pedicles 
and laminae (Fig. 2.19): 

■ The two pedicles are bony pillars that attach the verte¬ 
bral arch to the vertebral body. 

■ The two laminae are flat sheets of bone that extend 
from each pedicle to meet in the midline and form the 
roof of the vertebral arch. 

A spinous process projects posteriorly and inferiorly 
from the junction of the two laminae and is a site for 
muscle and ligament attachment. 

A transverse process extends posterolaterally from 
the junction of the pedicle and lamina on each side and is 
a site for articulation with ribs in the thoracic region. 

Also projecting from the region where the pedicles 
join the laminae are superior and inferior articular 
processes (Fig. 2.19), which articulate with the inferior 
and superior articular processes, respectively, of adjacent 
vertebrae. 


Superior articular process Superior vertebral notch 



Inferior articular process Inferior vertebral notch 

Superolateral oblique view 


68 
















Regional anatomy • Skeletal Framework 


2 


Between the vertebral body and the origin of the artic¬ 
ular processes, each pedicle is notched on its superior 
and inferior surfaces. These superior and inferior ver¬ 
tebral notches participate in forming intervertebral 
foramina. 

Cervical vertebrae 

The seven cervical vertebrae are characterized by their 
small size and by the presence of a foramen in each trans¬ 
verse process. A typical cervical vertebra has the following 
features (Fig. 2.20A): 


■ The vertebral body is short in height and square shaped 
when viewed from above and has a concave superior 
surface and a convex inferior surface. 

■ Each transverse process is trough shaped and perforated 
by a round foramen transversarium. 

■ The spinous process is short and bifid. 

■ The vertebral foramen is triangular. 

The first and second cervical vertebrae—the atlas 
and axis—are specialized to accommodate movement of 
the head. 


Foramen transversarium Vertebral body 




Uncinate process 


^Transverse 

process 


Vertebral canal 


Spinous process 


Foramen 

transversarium 


Spinous process 


A Superior view 

Fig. 2.20 Regional vertebrae. A. Typical cervical vertebra. 


Anterior view 


Continued 


69 










Back 


Atlas (Cl vertebra) and Axis (CM vertebra) 




Transverse ligament of atlas 


Anterior tubercle 
Facet for dens 


Posterior arch 


Atlas (Cl vertebra) 

Anterior arch 

Lateral mass 

process 


Foramen 

transversarium 


Facet for occipital condyle 
Posterior tubercle 


B 




Superior view 


Tectorial membrane (upper part 
of posterior longitudinal ligament) 


Superior view 


Apical ligament 
of dens 


Atlas (Cl 
vertebra) 
and Axis 
(CM 

vertebra) 
and base 


Alar 

ligaments 

Posterior 

longitudinal 

ligament 


Facets for 
attachment of 


alar ligaments 


of skull 


Dens 


Transverse ligament of atlas 

Inferior longitudinal 
Axis (CM vertebra) band of cruciform 
ligament 


Dens 


Superior view 


Posterior view 


Posterosuperior view 



Demifacet for articulation 
with head of its own rib 


Vertebral body 


Facet for articulation 
with tubercle of 
its own rib 


Mammillary 

process 


Demifacet for articulation 
with head of rib below 


Transverse 

process 


Transverse 

process 


Spinous 

process 


Spinous 

process 


C Superior view 


Lateral view 


D Superior view 


Fig. 2.20, cont’d B. Atlas and axis. C. Typical thoracic vertebra. D. Typical lumbar vertebra. 

















Regional anatomy • Skeletal Framework 


2 




Posterior sacral 
foramina 


Incomplete 
sacral canal 


-Anterior sacral 
foramina 


Facet for 
articulation 
with pelvic bone 


E 


Anterior view 


Dorsolateral view 


F 


Coccygeal cornu 



Posterior view 


Fig. 2.20, cont’d E. Sacrum. F. Coccyx. 


Atlas and axis 

Vertebra Cl (the atlas) articulates with the head (Fig. 
2.21). Its major distinguishing feature is that it lacks a 
vertebral body (Fig. 2.2OB). In fact, the vertebral body of 
Cl fuses onto the body of CII during development to become 
the dens of CII. As a result, there is no intervertebral disc 


Inferior articular facet 
on lateral mass of Cl 



facet of CII 


Fig. 2.21 Radiograph showing Cl (atlas) and CII (axis) vertebrae. 
Open mouth, anteroposterior (odontoid peg) view. 


between Cl and CII. When viewed from above, the atlas is 
ring shaped and composed of two lateral masses inter¬ 
connected by an anterior arch and a posterior arch. 

Each lateral mass articulates above with an occipital 
condyle of the skull and below with the superior articular 
process of vertebra CII (the axis). The superior articular 
surfaces are bean shaped and concave, whereas the infe¬ 
rior articular surfaces are almost circular and flat. 

The atlanto-occipital joint allows the head to nod up 
and down on the vertebral column. 

The posterior surface of the anterior arch has an articu¬ 
lar facet for the dens, which projects superiorly from the 
vertebral body of the axis. The dens is held in position by a 
strong transverse ligament of atlas posterior to it and 
spanning the distance between the oval attachment facets 
on the medial surfaces of the lateral masses of the atlas. 

The dens acts as a pivot that allows the atlas and 
attached head to rotate on the axis, side to side. 

The transverse processes of the atlas are large and pro¬ 
trude further laterally than those of the other cervical ver¬ 
tebrae and act as levers for muscle action, particularly for 
muscles that move the head at the atlanto-axial joints. 

The axis is characterized by the large tooth-like 
dens, which extends superiorly from the vertebral body 
(Figs. 2.2OB and 2.21). The anterior surface of the dens 
has an oval facet for articulation with the anterior arch of 
the atlas. 

The two superolateral surfaces of the dens possess cir¬ 
cular impressions that serve as attachment sites for strong 
alar ligaments, one on each side, which connect the dens 
to the medial surfaces of the occipital condyles. These alar 
ligaments check excessive rotation of the head and atlas 
relative to the axis. 71 























Back 


Thoracic vertebrae 

The twelve thoracic vertebrae are all characterized by their 
articulation with ribs. A typical thoracic vertebra has two 
partial facets (superior and inferior costal facets) on each 
side of the vertebral body for articulation with the head 
of its own rib and the head of the rib below (Fig. 2.20C). 
The superior costal facet is much larger than the inferior 
costal facet. 

Each transverse process also has a facet (transverse 
costal facet) for articulation with the tubercle of its own 
rib. The vertebral body of the vertebra is somewhat heart 
shaped when viewed from above, and the vertebral foramen 
is circular. 

Lumbar vertebrae 

The five lumbar vertebrae are distinguished from vertebrae 
in other regions by their large size (Fig. 2.20D). Also, they 
lack facets for articulation with ribs. The transverse pro¬ 
cesses are generally thin and long, with the exception of 
those on vertebra LV, which are massive and somewhat 
cone shaped for the attachment of iliolumbar ligaments 
to connect the transverse processes to the pelvic bones. 

The vertebral body of a typical lumbar vertebra is cylin¬ 
drical and the vertebral foramen is triangular in shape and 
larger than in the thoracic vertebrae. 

Sacrum 

The sacrum is a single bone that represents the five fused 
sacral vertebrae (Fig. 2.20E). It is triangular in shape with 
the apex pointed inferiorly, and is curved so that it has a 
concave anterior surface and a correspondingly convex 
posterior surface. It articulates above with vertebra LV 


and below with the coccyx. It has two large L-shaped 
facets, one on each lateral surface, for articulation with the 
pelvic bones. 

The posterior surface of the sacrum has four pairs of 
posterior sacral foramina, and the anterior surface has 
four pairs of anterior sacral foramina for the passage of 
the posterior and anterior rami, respectively, of SI to S4 
spinal nerves. 

The posterior wall of the vertebral canal may be incom¬ 
plete near the inferior end of the sacrum. 

Coccyx 

The coccyx is a small triangular bone that articulates with 
the inferior end of the sacrum and represents three to four 
fused coccygeal vertebrae (Fig. 2.2OF). It is characterized 
by its small size and by the absence of vertebral arches and 
therefore a vertebral canal. 

Intervertebral foramina 

Intervertebral foramina are formed on each side between 
adjacent parts of vertebrae and associated intervertebral 
discs (Fig. 2.22). The foramina allow structures, such as 
spinal nerves and blood vessels, to pass in and out of the 
vertebral canal. 

An intervertebral foramen is formed by the inferior ver¬ 
tebral notch on the pedicle of the vertebra above and the 
superior vertebral notch on the pedicle of the vertebra 
below. The foramen is bordered: 

■ posteriorly by the zygapophysial joint between the artic¬ 
ular processes of the two vertebrae, and 



Inferior vertebral notch 


Zygapophysial joint 


Intervertebral foramen 


Intervertebral disc 


Superior vertebral notch 


Fig. 2.22 Intervertebral foramen. 










Regional anatomy • Skeletal Framework 


2 


■ anteriorly by the intervertebral disc and adjacent verte¬ 
bral bodies. 

Each intervertebral foramen is a confined space sur¬ 
rounded by bone and ligament, and by joints. Pathology in 
any of these structures, and in the surrounding muscles, 
can affect structures within the foramen. 

Posterior spaces between vertebral arches 

In most regions of the vertebral column, the laminae and 
spinous processes of adjacent vertebrae overlap to form a 


reasonably complete bony dorsal wall for the vertebral 
canal. However, in the lumbar region, large gaps exist 
between the posterior components of adjacent vertebral 
arches (Fig. 2.23). These gaps between adjacent laminae 
and spinous processes become increasingly wide from ver¬ 
tebra LI to vertebra LV. The spaces can be widened further 
by flexion of the vertebral column. These gaps allow rela¬ 
tively easy access to the vertebral canal for clinical 
procedures. 



Lamina 


Spinous process 


Spinous process 
Lamina 


Space between 
adjacent laminae 


Fig. 2.23 Spaces between adjacent vertebral arches in the lumbar region. 


73 






















Back 


In the clinic 

Spina bifida 

Spina bifida is a disorder in which the two sides of 
vertebral arches, usually in lower vertebrae, fail to fuse 
during development, resulting in an "open" vertebral 
canal (Fig. 2.24). There are two types of spina bifida. 

■ The commonest type is spina bifida occulta, in which 
there is a defect in the vertebral arch of LV or SI. This 
defect occurs in as many as 10% of individuals and 
results in failure of the posterior arch to fuse in the 
midline. Clinically, the patient is asymptomatic, 
although physical examination may reveal a tuft of 
hair over the spinous processes. 

■ The more severe form of spina bifida involves 
complete failure of fusion of the posterior arch at 
the lumbosacral junction, with a large outpouching 
of the meninges. This may contain cerebrospinal 
fluid (a meningocele) or a portion of the spinal cord 
(a myelomeningocele). These abnormalities may 
result in a variety of neurological deficits, including 
problems with walking and bladder function. 


r Fourth ventricle 


Thoracic aorta vertebral 

p brain r spinous process 



Vertebral J Myelomeningocele 
body 


Fig. 2.24 TTweighted MR image in the sagittal plane 
demonstrating a lumbosacral myelomeningocele. There is an 
absence of laminae and spinous processes in the lumbosacral 
region. 


In the clinic 

Vertebroplasty 

Vertebroplasty is a new technique in which the body of a 
vertebra can be filled with bone cement (typically methyl 
methacrylate). The indications for the technique include 
vertebral body collapse and pain from the vertebral body, 
which may be secondary to tumor infiltration. The 
procedure is most commonly performed for osteoporotic 
wedge fractures, which are a considerable cause of 
morbidity and pain in older patients. 

Osteoporotic wedge fractures typically occur in the 
thoracolumbar region, and the approach to performing 


vertebroplasty is novel and relatively straightforward. The 
procedure is performed under sedation or light general 
anesthetic. Using X-ray guidance the pedicle is identified 
on the anteroposterior image. A metal cannula is placed 
through the pedicle into the vertebral body. Liquid bone 
cement is injected via the cannula into the vertebral body 
(see Fig. 1.18, p. 17). The function of the bone cement is 
two-fold. First, it increases the strength of the vertebral 
body and prevents further loss of height. Furthermore, as 
the bone cement sets, there is a degree of heat generated 
that is believed to disrupt pain nerve endings. 



Regional anatomy • Skeletal Framework 


2 


In the clinic 
Scoliosis 

Scoliosis is an abnormal lateral curvature of the vertebral 
column (Fig. 2.25). 

A true scoliosis involves not only the curvature 
(right- or left-sided) but also a rotational element of one 
vertebra upon another. 

The commonest types of scoliosis are those for which 
we have little understanding about how or why they 
occur and are termed idiopathic scoliosis. These are never 
present at birth and tend to occur in either the infantile, 
juvenile, or adolescent age groups. The vertebral bodies 
and posterior elements (pedicles and laminae) are normal 
in these patients. 

When a scoliosis is present from birth (congenital 
scoliosis) it is usually associated with other developmental 


abnormalities. In these patients, there is a strong 
association with other abnormalities of the chest wall, 
genitourinary tract, and heart disease. This group of 
patients needs careful evaluation by many specialists. 

A rare but important group of scoliosis is that in which 
the muscle is abnormal. Muscular dystrophy is the 
commonest example. The abnormal muscle does not 
retain the normal alignment of the vertebral column, and 
curvature develops as a result. A muscle biopsy is needed 
to make the diagnosis. 

Other disorders that can produce scoliosis include 
bone tumors, spinal cord tumors, and localized disc 
protrusions. 



Fig. 2.25 Severe scoliosis. A. Radiograph, anteroposterior view. B. Volume-rendered CT, anterior view. 


75 








Back 


In the clinic 

Kyphosis 

Kyphosis is abnormal curvature of the vertebral column in 
the thoracic region, producing a "hunchback" deformity. 
This condition occurs in certain disease states, the most 
dramatic of which is usually secondary to tuberculosis 
infection of a thoracic vertebral body, where the kyphosis 
becomes angulated at the site of the lesion. This produces 


the gibbus deformity, a deformity that was prevalent 
before the use of antituberculous medication. 

Lordosis 

Lordosis is abnormal curvature of the vertebral column in 
the lumbar region, producing a swayback deformity. 


In the clinic 

Variation in vertebral numbers 

There are usually seven cervical vertebrae, although 
in certain diseases these may be fused. Fusion of 
cervical vertebrae (Fig. 2.26A) can be associated with 
other abnormalities, for example Klippel-Feil syndrome, 
in which there is fusion of vertebrae Cl and Cll or CV 
and CVI, and may be associated with a high-riding 
scapula (Sprengel's shoulder) and cardiac 
abnormalities. 



Fused bodies of cervical vertebrae 


Variations in the number of thoracic vertebrae also are 
well described. 

One of the commonest abnormalities in the lumbar 
vertebrae is a partial fusion of vertebra LVwith the sacrum 
(sacralization of the lumbar vertebra). Partial separation of 
vertebra SI from the sacrum (lumbarization of first sacral 
vertebra) may also occur (Fig. 2.26B). 

A hemivertebra occurs when a vertebra develops only 
on one side (Fig. 2.26B). 

Hemivertebra 

_I_ 


B 


I 

Partial lumbarization of first sacral vertebra 


Fig. 2.26 Variations in vertebral number. A. Fused vertebral bodies of cervical vertebrae. B. Hemivertebra. 



Regional anatomy • Joints 


2 


In the clinic 

The vertebrae and cancer 

The vertebrae are common sites for metastatic disease 
(secondary spread of cancer cells). When cancer cells grow 
within the vertebral bodies and the posterior elements, 
they destroy the mechanical properties of the bone. A 


minor injury may therefore lead to vertebral collapse. 
Importantly, vertebrae that contain extensive metastatic 
disease may extrude fragments of tumor into the 
vertebral canal, compressing nerves and the spinal cord. 


In the clinic 

Osteoporosis 

Osteoporosis is a pathophysiologic condition in which 
bone quality is normal but the quantity of bone is 
deficient. It is a metabolic bone disorder that commonly 
occurs in women in their 50s and 60s and in men in 
their 70s. 

Many factors influence the development of 
osteoporosis, including genetic predetermination, level of 
activity and nutritional status, and, in particular, estrogen 
levels in women. 

Typical complications of osteoporosis include "crush" 
vertebral body fractures, distal fractures of the radius, and 
hip fractures. 


With increasing age and poor-quality bone, patients 
are more susceptible to fracture. Healing tends to be 
impaired in these elderly patients, who consequently 
require long hospital stays and prolonged rehabilitation. 

Patients likely to develop osteoporosis can be 
identified by dual-photon X-ray absorptiometry (DXA) 
scanning. Low-dose X-rays are passed through the bone, 
and by counting the number of photons detected and 
knowing the dose given, the number of X-rays absorbed 
by the bone can be calculated. The amount of X-ray 
absorption can be directly correlated with the bone mass, 
and this can be used to predict whether a patient is at risk 
for osteoporotic fractures. 


JOINTS 

Joints between vertebrae in the back 

The two major types of joints between vertebrae are: 

■ symphyses between vertebral bodies (Fig. 2.27), and 

■ synovial joints between articular processes (Fig. 2.28). 

A typical vertebra has a total of six joints with adjacent 
vertebrae: four synovial joints (two above and two below) 
and two symphyses (one above and one below). Each sym¬ 
physis includes an intervertebral disc. 

Although the movement between any two vertebrae is 
limited, the summation of movement among all vertebrae 
results in a large range of movement by the vertebral 
column. 

Movements by the vertebral column include flexion, 
extension, lateral flexion, rotation, and circumduction. 

Movements by vertebrae in a specific region (cervical, 
thoracic, and lumbar) are determined by the shape and 
orientation of joint surfaces on the articular processes and 
on the vertebral bodies. 



Layer of 

hyaline 

cartilage 


77 












Cervical 



Back 



“Sloped from anterior 
to posterior” 

Zygapophysial joint 


Lateral view 



Lateral view 


Thoracic 

“Vertical” 

Zygapophysial joint 



Lumbar 

“Wrapped” 


Lateral view 


Zygapophysial joint 



Symphyses between vertebral bodies 
(intervertebral discs) 

The symphysis between adjacent vertebral bodies is formed 
by a layer of hyaline cartilage on each vertebral body and 
an intervertebral disc, which lies between the layers. 

The intervertebral disc consists of an outer anulus 
fibrosus, which surrounds a central nucleus pulposus (Fig. 
2.27). 

■ The anulus fibrosus consists of an outer ring of col¬ 
lagen surrounding a wider zone of fibrocartilage 
arranged in a lamellar configuration. This arrangement 
of fibers limits rotation between vertebrae. 

■ The nucleus pulposus fills the center of the interver¬ 
tebral disc, is gelatinous, and absorbs compression forces 
between vertebrae. 

Degenerative changes in the anulus fibrosus can lead to 
herniation of the nucleus pulposus. Posterolateral hernia¬ 
tion can impinge on the roots of a spinal nerve in the 
intervertebral foramen. 

Joints between vertebral arches 
(zygapophysial joints) 

The synovial joints between superior and inferior articular 
processes on adjacent vertebrae are the zygapophysial 
joints (Fig. 2.28). A thin articular capsule attached to the 
margins of the articular facets encloses each joint. 

In cervical regions, the zygapophysial joints slope inte¬ 
riorly from anterior to posterior. This orientation facilitates 
flexion and extension. In thoracic regions, the joints are 
oriented vertically and limit flexion and extension, but 
facilitate rotation. In lumbar regions, the joint surfaces are 
curved and adjacent processes interlock, thereby limiting 
range of movement, though flexion and extension are still 
major movements in the lumbar region. 

"Uncovertebral" joints 

The lateral margins of the upper surfaces of typical cervi¬ 
cal vertebrae are elevated into crests or lips termed unci¬ 
nate processes. These may articulate with the body of the 
vertebra above to form small “uncovertebral” synovial 
joints (Fig. 2.29). 


Superior view 

Fig. 2.28 Zygapophysial joints. 


78 













Regional anatomy • Joints 


2 










Uncovertebral joint 
Uncinate process 


Fig. 2.29 Uncovertebral joint. 


In the clinic 
Back pain 

Back pain is an extremely common disorder. It can be 
related to mechanical problems or to disc protrusion 
impinging on a nerve. In cases involving discs, it may 
be necessary to operate and remove the disc that is 
pressing on the nerve. 

Not infrequently, patients complain of pain and no 
immediate cause is found; the pain is therefore 
attributed to mechanical discomfort, which may be 
caused by degenerative disease. One of the treatments 
is to pass a needle into the facet joint and inject it with 
local anesthetic and corticosteroid. 


In the clinic 

Herniation of intervertebral discs 

The discs between the vertebrae are made up of a central 
portion (the nucleus pulposus) and a complex series of 
fibrous rings (anulus fibrosus). A tear can occur within 
the anulus fibrosus through which the material of the 
nucleus pulposus can track. After a period of time, this 
material may track into the vertebral canal or into the 
intervertebral foramen to impinge on neural structures 


(Fig. 2.30). This is a common cause of back pain. A disc 
may protrude posteriorly to directly impinge on the cord 
or the roots of the lumbar nerves, depending on the level, 
or may protrude posterolaterally adjacent to the pedicle 
and impinge on the descending root. 

In cervical regions of the vertebral column, cervical disc 
protrusions often become ossified and are termed disc 
osteophyte bars. 




Vertebral canal containing CSF 
and cauda equina 


LIV vertebra 


Disc protrusion 


Psoas 


Meningeal sac containing 
CSF and cauda equina 


B 

Disc protrusion 


Facet 


Fig. 2.30 Disc protrusion. T2-weighted magnetic resonance images of the lumbar region of the vertebral column. A. Sagittal plane. 
B. Axial plane. 


79 














Back 


In the clinic 
Joint diseases 

Some diseases have a predilection for synovial joints 
rather than symphyses. A typical example is rheumatoid 
arthritis, which primarily affects synovial joints and 
synovial bursae, resulting in destruction of the joint and 
its lining. Symphyses are usually preserved. 


LIGAMENTS 

Joints between vertebrae are reinforced and supported by 
numerous ligaments, which pass between vertebral bodies 
and interconnect components of the vertebral arches. 

Anterior and posterior 
longitudinal ligaments 

The anterior and posterior longitudinal ligaments are on 
the anterior and posterior surfaces of the vertebral bodies 
and extend along most of the vertebral column (Fig. 2.31). 

The anterior longitudinal ligament is attached 
superiorly to the base of the skull and extends inferiorly to 
attach to the anterior surface of the sacrum. Along its 
length it is attached to the vertebral bodies and interverte¬ 
bral discs. 

The posterior longitudinal ligament is on the poste¬ 
rior surfaces of the vertebral bodies and lines the anterior 
surface of the vertebral canal. Like the anterior longitudi¬ 
nal ligament, it is attached along its length to the vertebral 
bodies and intervertebral discs. The upper part of the pos¬ 
terior longitudinal ligament that connects CII to the intra¬ 
cranial aspect of the base of the skull is termed the tectorial 
membrane (see Fig. 2.2OB). 


Posterior longitudinal ligament 



Fig. 2.31 Anterior and posterior longitudinal ligaments of 
vertebral column. 


Ligamenta flava 

The ligamenta flava, on each side, pass between the 
laminae of adjacent vertebrae (Fig. 2.32). These thin, 
broad ligaments consist predominantly of elastic tissue 
and form part of the posterior surface of the vertebral 






















Regional anatomy • Ligaments 


2 


Superior 

Ligamenta flava 



Inferior 

Fig. 2.32 Ligamenta flava. 


Superior 



Ligamenta flava 


Inferior Vertebral canal 


Posterior 


canal. Each ligamentum flavum runs between the poste¬ 
rior surface of the lamina on the vertebra below to the 
anterior surface of the lamina of the vertebra above. The 
ligamenta flava resist separation of the laminae in flexion 
and assist in extension back to the anatomical position. 

Supraspinous ligament 
and ligamentum nuchae 

The supraspinous ligament connects and passes along 
the tips of the vertebral spinous processes from vertebra 
CVII to the sacrum (Fig. 2.33). From vertebra CVII to 
the skull, the ligament becomes structurally distinct 
from more caudal parts of the ligament and is called the 
ligamentum nuchae. 

The ligamentum nuchae is a triangular, sheet-like 
structure in the median sagittal plane: 

■ The base of the triangle is attached to the skull, from the 
external occipital protuberance to the foramen magnum. 

■ The apex is attached to the tip of the spinous process of 
vertebra CVII. 

■ The deep side of the triangle is attached to the posterior 
tubercle of vertebra Cl and the spinous processes of the 
other cervical vertebrae. 

The ligamentum nuchae supports the head. It resists 
flexion and facilitates returning the head to the anatomical 



















Back 


position. The broad lateral surfaces and the posterior edge 
of the ligament provide attachment for adjacent muscles. 


Interspinous ligaments 

Interspinous ligaments pass between adjacent vertebral 
spinous processes (Fig. 2.34). They attach from the base to 
the apex of each spinous process and blend with the supra¬ 
spinous ligament posteriorly and the ligamenta flava ante¬ 
riorly on each side. 


In the clinic 

Ligamenta flava 

The ligamenta flava are important structures within the 
vertebral canal. In degenerative conditions of the 
vertebral column, the ligamenta flava may hypertrophy. 
This is often associated with hypertrophy and arthritic 
change of the zygapophysial joints. In combination, 
zygapophysial joint hypertrophy, ligamenta flava 
hypertrophy, and a mild disc protrusion can reduce the 
dimensions of the vertebral canal, producing the 
syndrome of spinal stenosis. 



Ligamentum flavum 


Supraspinous ligament 



Interspinous ligament 


Ligamentum flavum 
Fig. 2.34 Interspinous ligaments. 


Supraspinous ligament 


In the clinic 

Vertebral fractures 

Vertebral fractures can occur anywhere along the 
vertebral column. In most instances, the fracture will heal 
under appropriate circumstances. At the time of injury, 
it is not the fracture itself but related damage to the 
contents of the vertebral canal and the surrounding 
tissues that determines the severity of the patient's 
condition. 

Vertebral column stability is divided into three arbitrary 
clinical "columns": the anterior column consists of the 
vertebral bodies and the anterior longitudinal ligament; 
the middle column comprises the vertebral body and the 
posterior longitudinal ligament; and the posterior 
column is made up of the ligamenta flava, interspinous 
ligaments, supraspinous ligaments, and the ligamentum 
nuchae in the cervical vertebral column. 

Destruction of one of the clinical columns is usually 
a stable injury requiring little more than rest and 


appropriate analgesia. Disruption of two columns is 
highly likely to be unstable and requires fixation and 
immobilization. A three-column spinal injury usually 
results in a significant neurological event and requires 
fixation to prevent further extension of the neurological 
defect and to create vertebral column stability. 

At the craniocervical junction, a complex series of 
ligaments create stability. If the traumatic incident 
disrupts craniocervical stability, the chances of a 
significant spinal cord injury are extremely high. The 
consequences are quadriplegia. In addition, respiratory 
function may be compromised by paralysis of the phrenic 
nerve (which arises from spinal nerves C3 to C5), and 
severe hypotension (low blood pressure) may result from 
central disruption of the sympathetic part of the 
autonomic division of the nervous system. 

Mid and lower cervical vertebral column disruption 
may produce a range of complex neurological problems 


















Regional anatomy • Ligaments 


2 


In the clinic—cont'd 


involving the upper and lower limbs, although below 
the level of C5, respiratory function is unlikely to be 
compromised. 

Lumbar vertebral column injuries are rare. When they 
occur, they usually involve significant force. Knowing that 
a significant force is required to fracture a vertebra, one 
must assess the abdominal organs and the rest of the axial 



Pedicle Pars interarticularis 


skeleton for further fractures and visceral rupture. 

Vertebral injuries may also involve the soft tissues and 
supporting structures between the vertebrae. Typical 
examples of this are the unifacetal and bifacetal cervical 
vertebral dislocations that occur in hyperflexion injuries. 

Pars interarticularis fractures 

The pars interarticularis is a clinical term to describe the 
specific region of a vertebra between the superior and 
inferior facet (zygapophysial) joints (Fig. 2.35A). This 
region is susceptible to trauma, especially in athletes. 

If a fracture occurs around the pars interarticularis, the 
vertebral body may slip anteriorly and compress the 
vertebral canal. 

The most common sites for pars interarticularis 
fractures are the LIV and LV levels (Fig. 2.35B). (Clinicians 
often refer to parts of the back in shorthand terms that 
are not strictly anatomical; for example, facet joints and 
apophyseal joints are terms used instead of zygapophysial 
joints, and spinal column is used instead of vertebral 
column.) 

It is possible for a vertebra to slip anteriorly upon its 
inferior counterpart without a pars interarticularis fracture. 
Usually this is related to abnormal anatomy of the facet 
joints, facet joint degenerative change. This disorder is 
termed spondylolisthesis. 


Pars fracture 



Fig. 2.35 Radiograph of lumbar region of vertebral column, oblique view (“Scottie dog”). A. Normal radiograph of lumbar region of 
vertebral column, oblique view. In this view, the transverse process (nose), pedicle (eye), superior articular process (ear), inferior 
articular process (front leg), and pars interarticularis (neck) resemble a dog. A fracture of the pars interarticularis is visible as a break in 
the neck of the dog, or the appearance of a collar. B. Fracture of pars interarticularis. 


83 






Back 


In the clinic 

Surgical procedures on the back 

Discectomy/laminectomy 

A prolapsed intervertebral disc may impinge upon the 
meningeal (thecal) sac, cord, and most commonly the 
nerve root, producing symptoms attributable to that 
level. In some instances the disc protrusion will undergo 
a degree of involution that may allow symptoms to 
resolve without intervention. In some instances pain, 
loss of function, and failure to resolve may require 
surgery to remove the disc protrusion. 

It is of the utmost importance that the level of the 
disc protrusion is identified before surgery. This may 
require MRI scanning and on-table fluoroscopy to 
prevent operating on the wrong level. A midline 
approach to the right or to the left of the spinous 
processes will depend upon the most prominent site of 
the disc bulge. In some instances removal of the lamina 
will increase the potential space and may relieve 
symptoms. Some surgeons perform a small fenestration 
(windowing) within the ligamentum flavum. This 
provides access to the canal. The meningeal sac and its 
contents are gently retracted, exposing the nerve root 
and the offending disc. The disc is dissected free, 
removing its effect on the nerve root and the canal. 

Spinal Fusion 

Spinal fusion is performed when it is necessary to fuse 
one vertebra with the corresponding superior or inferior 
vertebra, and in some instances multilevel fusion may 
be necessary. Indications are varied, though they 
include stabilization after fracture, stabilization related 
to tumor infiltration, and stabilization when mechanical 
pain is produced either from the disc or from the 
posterior elements. 

There are a number of surgical methods in which a 
fusion can be performed, through either a posterior 
approach and fusing the posterior elements, an anterior 
approach by removal of the disc and either disc 
replacement or anterior fusion, or in some instances a 
360° fusion where the posterior elements and the 
vertebral bodies are fused. 


BACK MUSCULATURE 

Muscles of the back are organized into superficial, interme¬ 
diate, and deep groups. 

Muscles in the superficial and intermediate groups are 
extrinsic muscles because they originate embryologically 
from locations other than the back. They are innervated by 
anterior rami of spinal nerves: 

■ The superficial group consists of muscles related to and 
involved in movements of the upper limb. 

■ The intermediate group consists of muscles attached to 
the ribs and may serve a respiratory function. 

Muscles of the deep group are intrinsic muscles because 
they develop in the back. They are innervated by posterior 
rami of spinal nerves and are directly related to movements 
of the vertebral column and head. 

Superficial group of back muscles 

The muscles in the superficial group are immediately deep 
to the skin and superficial fascia (Figs. 2.36 to 2.39). They 
attach the superior part of the appendicular skeleton (clav¬ 
icle, scapula, and humerus) to the axial skeleton (skull, 
ribs, and vertebral column). Because these muscles are pri¬ 
marily involved with movements of this part of the appen¬ 
dicular skeleton, they are sometimes referred to as the 
appendicular group. 

Muscles in the superficial group include the trapezius, 
latissimus dorsi, rhomboid major, rhomboid minor, and 
levator scapulae. The rhomboid major, rhomboid minor, 
and levator scapulae muscles are located deep to the trape¬ 
zius muscle in the superior part of the back. 



Regional anatomy • Back Musculature 


2 



Fig. 2.36 Superficial group of back muscles—trapezius and latissimus dorsi. 


85 

























Back 



Trapezius 


Latissimus dorsi 


Ligamentum nuchae 


Levator scapulae 

Rhomboid minor 


Rhomboid major 


Fig. 2.37 Superficial group of back muscles—trapezius and latissimus dorsi, with rhomboid major, rhomboid minor, and levator scapulae 
located deep to trapezius in the superior part of the back. 




















Regional anatomy • Bock Musculature 


2 


Trapezius 

Each trapezius muscle is flat and triangular, with the base 
of the triangle situated along the vertebral column (the 
muscle’s origin) and the apex pointing toward the tip of the 
shoulder (the muscle’s insertion) (Fig. 2.37 and Table 2.1). 
The muscles on both sides together form a trapezoid. 

The superior fibers of the trapezius, from the skull and 
upper portion of the vertebral column, descend to attach 
to the lateral third of the clavicle and to the acromion 
of the scapula. Contraction of these fibers elevates the 
scapula. In addition, the superior and inferior fibers work 


together to rotate the lateral aspect of the scapula upward, 
which needs to occur when raising the upper limb above 
the head. 

Motor innervation of the trapezius is by the accessory 
nerve [XI], which descends from the neck onto the deep 
surface of the muscle (Fig. 2.38). Proprioceptive fibers from 
the trapezius pass in the branches of the cervical plexus 
and enter the spinal cord at spinal cord levels C3 and C4. 

The blood supply to the trapezius is from the superficial 
branch of the transverse cervical artery, the acromial 
branch of the suprascapular artery, and the dorsal 
branches of posterior intercostal arteries. 



Latissimus dorsi 


Trapezius 


Levator scapulae 


Superficial branch of transverse cervical artery 


Accessory nerve [XI] 


Rhomboid minor 


Rhomboid major 


Fig. 2.38 Innervation and blood supply of trapezius. 


87 


















Back 



Fig. 2.39 Rhomboid muscles and levator scapulae. 



























Regional anatomy • Back Musculature 


2 


Table 2.1 Superficial (appendicular) group of back muscles 


Muscle 

Origin 

Insertion 

Innervation 

Function 

Trapezius 

Superior nuchal line, external 
occipital protuberance, 
ligamentum nuchae, spinous 
processes of CVII to TXII 

Lateral one third of 
clavicle, acromion, spine 
of scapula 

Motor—accessory nerve 
[XI]; proprioception—C3 
and C4 

Assists in rotating the scapula 
during abduction of humerus 
above horizontal; upper 
fibers elevate, middle fibers 
adduct, and lower fibers 
depress scapula 

Latissimus dorsi 

Spinous processes of TVII to 

LV and sacrum, iliac crest, 
ribs X to XII 

Floor of intertubercular 
sulcus of humerus 

Thoracodorsal nerve (C6 
to C8) 

Extends, adducts, and 
medially rotates humerus 

Levator scapulae 

Transverse processes of Cl to 
CIV 

Upper portion medial 
border of scapula 

C3 to C4 and dorsal 
scapular nerve (C4, C5) 

Elevates scapula 

Rhomboid major 

Spinous processes of Til to 

TV 

Medial border of scapula 
between spine and 
inferior angle 

Dorsal scapular nerve 
(C4, C5) 

Retracts (adducts) and 
elevates scapula 

Rhomboid minor 

Lower portion of 
ligamentum nuchae, spinous 
processes of CVII and TI 

Medial border of scapula 
at spine of scapula 

Dorsal scapular nerve 
(C4, C5) 

Retracts (adducts) and 
elevates scapula 


Latissimus dorsi 

Latissimus dorsi is a large, flat triangular muscle that 
begins in the lower portion of the back and tapers as it 
ascends to a narrow tendon that attaches to the humerus 
anteriorly (Figs. 2.36 to 2.39 and Table 2.1). As a result, 
movements associated with this muscle include extension, 
adduction, and medial rotation of the upper limb. The latis¬ 
simus dorsi can also depress the shoulder, preventing its 
upward movement. 

The thoracodorsal nerve of the brachial plexus inner¬ 
vates the latissimus dorsi muscle. Associated with this 
nerve is the thoracodorsal artery, which is the primary 
blood supply of the muscle. Additional small arteries come 
from dorsal branches of posterior intercostal and lumbar 
arteries. 

Levator scapulae 

Levator scapulae is a slender muscle that descends from 
the transverse processes of the upper cervical vertebrae to 
the upper portion of the scapula on its medial border at the 
superior angle (Fig. 2.37 and 2.39, and Table 2.1). It 


elevates the scapula and may assist other muscles in rotat¬ 
ing the lateral aspect of the scapula inferiorly. 

The levator scapulae is innervated by branches from the 
anterior rami of spinal nerves C3 and C4 and the dorsal 
scapular nerve, and its arterial supply consists of branches 
primarily from the transverse and ascending cervical 
arteries. 

Rhomboid minor and rhomboid major 

The two rhomboid muscles are inferior to levator scapulae 
(Fig. 2.39 and Table 2.1). Rhomboid minor is superior to 
rhomboid major, and is a small, cylindrical muscle that 
arises from the ligamentum nuchae of the neck and the 
spinous processes of vertebrae CVII and TI and attaches to 
the medial scapular border opposite the root of the spine 
of the scapula. 

The larger rhomboid major originates from the 
spinous processes of the upper thoracic vertebrae and 
attaches to the medial scapular border inferior to rhomboid 
minor. 

The two rhomboid muscles work together to retract or 
pull the scapula toward the vertebral column. With other 


89 



Back 


muscles they may also rotate the lateral aspect of the 
scapula inferiorly. 

The dorsal scapular nerve, a branch of the brachial 
plexus, innervates both rhomboid muscles (Fig. 2.40). 

Intermediate group of back muscles 

The muscles in the intermediate group of back muscles 
consist of two thin muscular sheets in the superior and 
inferior regions of the back, immediately deep to the 
muscles in the superficial group (Fig. 2.41 and Table 2.2). 
Fibers from these two serratus posterior muscles (serratus 
posterior superior and serratus posterior inferior) 
pass obliquely outward from the vertebral column to attach 
to the ribs. This positioning suggests a respiratory function, 


and at times, these muscles have been referred to as the 
respiratory group. 

Serratus posterior superior is deep to the rhomboid 
muscles, whereas serratus posterior inferior is deep to 
the latissimus dorsi. Both serratus posterior muscles are 
attached to the vertebral column and associated structures 
medially, and either descend (the fibers of the serratus pos¬ 
terior superior) or ascend (the fibers of the serratus pos¬ 
terior inferior) to attach to the ribs. These two muscles 
therefore elevate and depress the ribs. 

The serratus posterior muscles are innervated by seg¬ 
mental branches of anterior rami of intercostal nerves. 
Their vascular supply is provided by a similar segmental 
pattern through the intercostal arteries. 


Rhomboid minor 


Rhomboid major 


Levator scapulae 

Dorsal scapular nerve 

Superficial branch of transverse cervical artery 

Trapezius 



Deep branch of transverse 
cervical artery 


Latissimus dorsi 


Fig. 2.40 Innervation and blood supply of the rhomboid muscles. 






















Regional anatomy • Back Musculature 


2 



Serratus posterior superior 


Serratus posterior inferior 


Posterior layer of 
thoracolumbar fascia 


Fig. 2.41 Intermediate group of back muscles—serratus posterior muscles. 


Table 2.2 Intermediate (respiratory) group of back muscles 


Muscle 

Origin 

Insertion 

Innervation 

Function 

Serratus posterior 
superior 

Lower portion of ligamentum 
nuchae, spinous processes of 
CVII to Till, and supraspinous 
ligaments 

Upper border of ribs II 
to V just lateral to their 
angles 

Anterior rami of 
upper thoracic nerves 
(T2 to T5) 

Elevates ribs II to V 

Serratus posterior 

Spinous processes of TXI to 

Lower border of ribs IX 

Anterior rami of 

Depresses ribs IX to XII and 

inferior 

Llll and supraspinous 
ligaments 

to XII just lateral to their 
angles 

lower thoracic nerves 
(T9 to T12) 

may prevent lower ribs from 
being elevated when the 
diaphragm contracts 


91 















Back 


Deep group of back muscles 

The deep or intrinsic muscles of the back extend from 
the pelvis to the skull and are innervated by segmental 
branches of the posterior rami of spinal nerves. They 
include: 

■ the extensors and rotators of the head and neck— 
the splenius capitis and cervicis (spinotransversales 
muscles), 

■ the extensors and rotators of the vertebral column—the 
erector spinae and transversospinales, and 

■ the short segmental muscles—the interspinales and 
intertransversarii. 

The vascular supply to this deep group of muscles 
is through branches of the vertebral, deep cervical, occipi¬ 
tal, transverse cervical, posterior intercostal, subcostal, 
lumbar, and lateral sacral arteries. 

Thoracolumbar fascia 

The thoracolumbar fascia covers the deep muscles of 
the back and trunk (Fig. 2.42). This fascial layer is critical 
to the overall organization and integrity of the region: 

■ Superiorly, it passes anteriorly to the serratus posterior 
muscle and is continuous with deep fascia in the neck. 

■ In the thoracic region, it covers the deep muscles and 
separates them from the muscles in the superficial and 
intermediate groups. 

■ Medially, it attaches to the spinous processes of the tho¬ 
racic vertebrae and, laterally, to the angles of the ribs. 

The medial attachments of the latissimus dorsi and ser¬ 
ratus posterior inferior muscles blend into the thoracolum¬ 
bar fascia. In the lumbar region, the thoracolumbar fascia 
consists of three layers: 



Psoas major muscle 


Transversus 


Erector spinae muscles 


Latissimus dorsi 
muscle 


Thoracolumbar fascia 


•-Anterior layer 

- Middle layer 

- Posterior layer 


Fig. 2.42 Thoracolumbar fascia and the deep back muscles 
(transverse section). 


abdominal wall) and is attached medially to the trans¬ 
verse processes of the lumbar vertebrae—interiorly, it 
is attached to the iliac crest and, superiorly, it forms 
the lateral arcuate ligament for attachment of the 
diaphragm. 

The posterior and middle layers of the thoracolumbar 
fascia come together at the lateral margin of the erector 
spinae (Fig. 2.42). At the lateral border of the quadratus 
lumborum, the anterior layer joins them and forms the 
aponeurotic origin for the transversus abdominis muscle 
of the abdominal wall. 

Spinotransversales muscles 

The two spinotransversales muscles run from the spinous 
processes and ligamentum nuchae upward and laterally 
(Fig. 2.43 and Table 2.3): 


The posterior layer is thick and is attached to the spinous 
processes of the lumbar vertebrae and sacral vertebrae 
and to the supraspinous ligament—from these attach¬ 
ments, it extends laterally to cover the erector spinae. 
The middle layer is attached medially to the tips of the 
transverse processes of the lumbar vertebrae and inter- 
transverse ligaments—interiorly, it is attached to the 
iliac crest and, superiorly, to the lower border of rib XII. 
The anterior layer covers the anterior surface of the 
quadratus lumborum muscle (a muscle of the posterior 


■ The splenius capitis is a broad muscle attached to the 
occipital bone and mastoid process of the temporal 
bone. 

■ The splenius cervicis is a narrow muscle attached to the 
transverse processes of the upper cervical vertebrae. 

Together the spinotransversales muscles draw the head 
backward, extending the neck. Individually, each muscle 
rotates the head to one side—the same side as the contract¬ 
ing muscle. 











Regional anatomy • Back Musculature 


2 



Fig. 2.43 Deep group of back muscles—spinotransversales muscles (splenius capitis and splenius cervicis). 


Table 2.3 Spinotransversales muscles 


Muscle 

Origin 

Insertion 

Innervation 

Function 

Splenius capitis 

Lower half of ligamentum 
nuchae, spinous processes 
of CVII to TIV 

Mastoid process, skull 
below lateral one third of 
superior nuchal line 

Posterior rami of middle 
cervical nerves 

Together—draw head 
backward, extending neck; 
individually—draw and rotate 
head to one side (turn face to 
same side) 

Splenius cervicis 

Spinous processes of Till 
to TVI 

Transverse processes of 

Cl to cm 

Posterior rami of lower 
cervical nerves 

Together—extend neck; 
individually—draw and rotate 


head to one side (turn face to 
same side) 


Erector spinae muscles 

The erector spinae is the largest group of intrinsic back 
muscles. The muscles lie posterolaterally to the vertebral 
column between the spinous processes medially and 
the angles of the ribs laterally. They are covered in the 
thoracic and lumbar regions by thoracolumbar fascia and 
the serratus posterior inferior, rhomboid, and splenius 
muscles. The mass arises from a broad, thick tendon 


attached to the sacrum, the spinous processes of the 
lumbar and lower thoracic vertebrae, and the iliac crest 
(Fig. 2.44 and Table 2.4). It divides in the upper lumbar 
region into three vertical columns of muscle, each of 
which is further subdivided regionally (lumborum, thora¬ 
cis, cervicis, and capitis), depending on where the muscles 
attach superiorly. 


93 
















Back 


Splenius capitis 


Spinous process of CVII 


Spinalis 

Longissimus 

lliocostalis 


Iliac crest 



Ligamentum nuchae 

Longissimus capitis 

lliocostalis cervicis 
Longissimus cervicis 


Spinalis thoracis 
Longissimus thoracis 

lliocostalis thoracis 


lliocostalis lumborum 


Fig. 2.44 Deep group of back muscles—erector spinae muscles. 
































Regional anatomy • Back Musculature 


2 


Table 2.4 Erector spinae group of back muscles 

Muscle 

Origin 

Insertion 

Iliocostalis lumborum 

Sacrum, spinous processes of lumbar and lower two 
thoracic vertebrae and their supraspinous ligaments, 
and the iliac crest 

Angles of the lower six or seven ribs 

Iliocostalis thoracis 

Angles of the lower six ribs 

Angles of the upper six ribs and the transverse 
process of CVII 

Iliocostalis cervicis 

Angles of ribs III to VI 

Transverse processes of CIV to CVI 

Longissimus thoracis 

Blends with iliocostalis in lumbar region and is 
attached to transverse processes of lumbar vertebrae 

Transverse processes of all thoracic vertebrae and just 
lateral to the tubercles of the lower nine or ten ribs 

Longissimus cervicis 

Transverse processes of upper four or five thoracic 
vertebrae 

Transverse processes of Cll to CVI 

Longissimus capitis 

Transverse processes of upper four or five thoracic 
vertebrae and articular processes of lower three or 
four cervical vertebrae 

Posterior margin of the mastoid process 

Spinalis thoracis 

Spinous processes of TX orTXI to Lll 

Spinous processes of Tl to TVIII (varies) 

Spinalis cervicis 

Lower part of ligamentum nuchae and spinous 
process of CVII (sometimes Tl to Til) 

Spinous process of Cll (axis) 

Spinalis capitis 

Usually blends with semispinalis capitis 

With semispinalis capitis 


■ The outer or most laterally placed column of the erector 
spinae muscles is the iliocostalis, which is associated 
with the costal elements and passes from the common 
tendon of origin to multiple insertions into the angles 
of the ribs and the transverse processes of the lower 
cervical vertebrae. 

■ The middle or intermediate column is the longissimus, 
which is the largest of the erector spinae subdivision 
extending from the common tendon of origin to the 
base of the skull. Throughout this vast expanse, the 
lateral positioning of the longissimus muscle is in 
the area of the transverse processes of the various 
vertebrae. 

■ The most medial muscle column is the spinalis, which 
is the smallest of the subdivisions and interconnects the 
spinous processes of adjacent vertebrae. The spinalis is 
most constant in the thoracic region and is generally 
absent in the cervical region. It is associated with a 
deeper muscle (the semispinalis capitis) as the erector 
spinae group approaches the skull. 

The muscles in the erector spinae group are the primary 
extensors of the vertebral column and head. Acting bilat¬ 
erally, they straighten the back, returning it to the upright 
position from a flexed position, and pull the head posteri¬ 
orly. They also participate in controlling vertebral column 
flexion by contracting and relaxing in a coordinated 
fashion. Acting unilaterally, they bend the vertebral 
column laterally. In addition, unilateral contractions of 
muscles attached to the head turn the head to the actively 
contracting side. 


Transversospinales muscles 

The transversospinales muscles run obliquely upward and 
medially from transverse processes to spinous processes, 
filling the groove between these two vertebral projections 
(Fig. 2.45 and Table 2.5). They are deep to the erector 
spinae and consist of three major subgroups—the semispi¬ 
nalis, multifidus, and rotatores muscles. 

■ The semispinalis muscles are the most superficial col¬ 
lection of muscle fibers in the transversospinales group. 
These muscles begin in the lower thoracic region and 
end by attaching to the skull, crossing between four 
and six vertebrae from their point of origin to point of 
attachment. Semispinalis muscles are found in the tho¬ 
racic and cervical regions, and attach to the occipital 
bone at the base of the skull. 

■ Deep to the semispinalis is the second group of muscles, 
the multifidus. Muscles in this group span the length 
of the vertebral column, passing from a lateral point of 
origin upward and medially to attach to spinous pro¬ 
cesses and spanning between two and four vertebrae. 
The multifidus muscles are present throughout the 
length of the vertebral column but are best developed in 
the lumbar region. 

■ The small rotatores muscles are the deepest of the 
transversospinales group. They are present throughout 
the length of the vertebral column but are best devel¬ 
oped in the thoracic region. Their fibers pass upward 
and medially from transverse processes to spinous pro¬ 
cesses crossing two vertebrae (long rotators) or attach¬ 
ing to an adjacent vertebra (short rotators). 


95 



Back 



Spinous process of CVII 


Levatores costarum 
(short, long) 


Multifidus 


Intertransversarius 


Erector spinae 


Rectus capitis posterior minor 


Obliquus capitis superior 


Semispinalis thoracis 


Rotatores thoracis 
(short, long) 


Semispinalis capitis 


Rectus capitis posterior major 
Obliquus capitis inferior 


Fig. 2.45 Deep group of back muscles—transversospinales and segmental muscles. 





























Regional anatomy • Bock Musculature 


2 


Table 2.5 Transversospinales group of back muscles 

Muscle Origin 

Semispinalis thoracis Transverse processes of TVI to TX 


Semispinalis cervicis 
Semispinalis capitis 

Multifidus 


Rotatores lumborum 


Transverse processes of upper five or six thoracic vertebrae 

Transverse processes of Tl to TVI (or TVII) and CVII and 
articular processes of CIV to CVI 

Sacrum, origin of erector spinae, posterior superior iliac 
spine, mammillary processes of lumbar vertebrae, 
transverse processes of thoracic vertebrae, and articular 
processes of lower four cervical vertebrae 

Transverse processes of lumbar vertebrae 


Rotatores thoracis Transverse processes of thoracic vertebrae 


Rotatores cervicis Articular processes of cervical vertebrae 


Insertion 

Spinous processes of upper four thoracic and 
lower two cervical vertebrae 

Spinous processes of Cll (axis) to CV 

Medial area between the superior and inferior 
nuchal lines of occipital bone 

Base of spinous processes of all vertebrae from 
LV to Cll (axis) 


Spinous processes of lumbar vertebrae 
Spinous processes of thoracic vertebrae 
Spinous processes of cervical vertebrae 


When muscles in the transversospinales group contract 
bilaterally, they extend the vertebral column, an action 
similar to that of the erector spinae group. However, when 
muscles on only one side contract, they pull the spinous 
processes toward the transverse processes on that side, 
causing the trunk to turn or rotate in the opposite 
direction. 

One muscle in the transversospinales group, the semi¬ 
spinalis capitis, has a unique action because it attaches 
to the skull. Contracting bilaterally, this muscle pulls the 
head posteriorly, whereas unilateral contraction pulls the 
head posteriorly and turns it, causing the chin to move 
superiorly and turn toward the side of the contracting 
muscle. These actions are similar to those of the upper 
erector spinae. 

Segmental muscles 

The two groups of segmental muscles (Fig. 2.45 and Table 
2.6) are deeply placed in the back and innervated by pos¬ 
terior rami of spinal nerves. 

■ The first group of segmental muscles are the levatores 
costarum muscles, which arise from the transverse 


processes of vertebrae CVII and TI to TXI. They have an 
oblique lateral and downward direction and insert into 
the rib below the vertebra of origin in the area of the 
tubercle. Contraction elevates the ribs. 

■ The second group of segmental muscles are the true 
segmental muscles of the back—the interspinales, 
which pass between adjacent spinous processes, and the 
intertransversarii, which pass between adjacent 
transverse processes. These postural muscles stabilize 
adjoining vertebrae during movements of the vertebral 
column to allow more effective action of the large 
muscle groups. 


Suboccipital muscles 

A small group of deep muscles in the upper cervical region 
at the base of the occipital bone move the head. They 
connect vertebra Cl (the atlas) to vertebra CII (the axis) and 
connect both vertebrae to the base of the skull. Because 
of their location they are sometimes referred to as suboc¬ 
cipital muscles (Figs. 2.45 and 2.46 and Table 2.7). They 
include, on each side: 


Table 2.6 Segmental back muscles 


Muscle 

Origin 

Insertion 

Function 

Levatores costarum 

Short paired muscles arising from 
transverse processes of CVII to TXI 

The rib below vertebra of origin 
near tubercle 

Contraction elevates rib 

Interspinales 

Short paired muscles attached to the 
spinous processes of contiguous vertebrae, 
one on each side of the interspinous 
ligament 


Postural muscles that stabilize 
adjoining vertebrae during 
movements of vertebral column 

Intertransversarii 

Small muscles between the transverse 
processes of contiguous vertebrae 


Postural muscles that stabilize 
adjoining vertebrae during 
movements of vertebral column 


97 



Back 


Semispinalis capitis 


Rectus capitis posterior minor 


Obliquus capitis inferior 


Semispinalis capitis 


Splenius capitis 



Vertebral artery 
Posterior ramus of Cl 
Rectus capitis posterior major 


Spinous process of CM 

Semispinalis cervicis 

Longissimus capitis 


Obliquus capitis superior 


Splenius capitis 


Fig. 2.46 Deep group of back muscles—suboccipital muscles. This also shows the borders of the suboccipital triangle. 


Table 2.7 Suboccipital group of back muscles 


Muscle 

Origin 

Insertion 

Innervation 

Function 

Rectus capitis posterior 
major 

Spinous process of 
axis (CM) 

Lateral portion of occipital 
bone below inferior nuchal 
line 

Posterior ramus of Cl 

Extension of head; rotation of 
face to same side as muscle 

Rectus capitis posterior 
minor 

Posterior tubercle of 
atlas (Cl) 

Medial portion of occipital 
bone below inferior nuchal 
line 

Posterior ramus of Cl 

Extension of head 

Obliquus capitis superior 

Transverse process of 
atlas (Cl) 

Occipital bone between 
superior and inferior nuchal 
lines 

Posterior ramus of Cl 

Extension of head and bends 
it to same side 

Obliquus capitis inferior 

Spinous process of 
axis (CM) 

Transverse process of atlas 
(Cl) 

Posterior ramus of Cl 

Rotation of face to same side 


■ rectus capitis posterior major, 

■ rectus capitis posterior minor, 

■ obliquus capitis inferior, and 

■ obliquus capitis superior. 

Contraction of the suboccipital muscles extends the 
head at the atlanto-axial joint. 

The suboccipital muscles are innervated by the posterior 
ramus of the first cervical nerve, which enters the area 
between the vertebral artery and the posterior arch of the 
atlas (Fig. 2.46). The vascular supply to the muscles in this 
area is from branches of the vertebral and occipital arteries. 


The suboccipital muscles form the boundaries of the 
suboccipital triangle, an area that contains several 
important structures (Fig. 2.46): 

■ The rectus capitis posterior major muscle forms the 
medial border of the triangle. 

■ The obliquus capitis superior muscle forms the lateral 
border. 

■ The obliquus capitis inferior muscle forms the inferior 
border. 






















Regional anatomy • Spinal Cord 


2 


The contents of the area outlined by these muscles are 
the posterior ramus of Cl, the vertebral artery, and associ¬ 
ated veins. 


In the clinic 

Nerve injuries affecting superficial back muscles 

Weakness in the trapezius, caused by an interruption of 
the accessory nerve [XI], may appear as drooping of the 
shoulder, inability to raise the arm above the head 
because of impaired rotation of the scapula, or 
weakness in attempting to raise the shoulder 
(i.e., shrug the shoulder against resistance). 

A weakness in, or an inability to use, the latissimus 
dorsi, resulting from an injury to the thoracodorsal 
nerve, diminishes the capacity to pull the body upward 
while climbing or doing a pull-up. 

An injury to the dorsal scapular nerve, which 
innervates the rhomboids, may result in a lateral shift in 
the position of the scapula on the affected side (i.e., the 
normal position of the scapula is lost because of the 
affected muscle's inability to prevent antagonistic 
muscles from pulling the scapula laterally). 


SPINAL CORD 

The spinal cord extends from the foramen magnum to 
approximately the level of the disc between vertebrae LI 
and LII in adults, although it can end as high as vertebra 
TXII or as low as the disc between vertebrae LII and LIII 
(Fig. 2.47). In neonates, the spinal cord extends approxi¬ 
mately to vertebra LIII but can reach as low as vertebra LIV. 
The distal end of the cord (the conus medullaris) is cone 
shaped. A fine filament of connective tissue (the pial part 
of the filum terminale) continues inferiorly from the apex 
of the conus medullaris. 

The spinal cord is not uniform in diameter along its 
length. It has two major swellings or enlargements in 
regions associated with the origin of spinal nerves that 
innervate the upper and lower limbs. A cervical enlarge¬ 
ment occurs in the region associated with the origins of 
spinal nerves C5 to Tl, which innervate the upper limbs. 
A lumbosacral enlargement occurs in the region associ¬ 
ated with the origins of spinal nerves LI to S3, which 
innervate the lower limbs. 

The external surface of the spinal cord is marked by a 
number of fissures and sulci (Fig. 2.48): 

■ The anterior median fissure extends the length o f the 

anterior surface. 



99 
























Central canal 



Back 




Gray matter 


White matter- 


Posterolateral 

sulcus 


Posterior median 
sulcus 


Anterior 
median fissure 


Anterior median fissure 
Fig. 2.48 Features of the spinal cord. 


■ The posterior median sulcus extends along the pos¬ 
terior surface. 

■ The posterolateral sulcus on each side of the poste¬ 
rior surface marks where the posterior rootlets of spinal 
nerves enter the cord. 

Internally, the cord has a small central canal surrounded 

by gray and white matter: 

■ The gray matter is rich in nerve cell bodies, which form 
longitudinal columns along the cord, and in cross 
section these columns form a characteristic H-shaped 
appearance in the central regions of the cord. 

■ The white matter surrounds the gray matter and is rich 
in nerve cell processes, which form large bundles or 
tracts that ascend and descend in the cord to other 
spinal cord levels or carry information to and from 
the brain. 

Vasculature 

Arteries 



Posterior spinal artery 
Anterior spinal artery 


Segmental medullary 
arteries 

Vertebral artery 

Ascending cervical 
artery 

Deep cervical artery 
Costocervical trunk 
Thyrocervical trunk 
Subclavian artery 


Segmental medullary 
arteries (branch from 
segmental spinal 
artery) 

Segmental 
spinal artery 


Posterior intercostal 
artery 


Artery of Adamkiewicz 
(branch from 
segmental 
spinal artery) 


Segmental 
spinal artery 


Lateral sacral artery 


The arterial supply to the spinal cord comes from two 
100 sources (Fig. 2.49). It consists of: 


Fig. 2.49 Arteries that supply the spinal cord. A. Anterior view of 
spinal cord (not all segmental spinal arteries are shown). 

















































Regional anatomy • Spinal Cord 


2 


Anterior radicular artery 



Segmental spinal artery 


Left posterior 
intercostal artery 


Aorta 


Anterior radicular artery 


Segmental medullary artery 


Segmental spinal artery 


Posterior branch 
of right posterior 
intercostal artery 


Posterior radicular artery 


Posterior spinal arteries 

Posterior radicular artery 


Segmental 
spinal artery 


Posterior branch 
of left posterior 
intercostal artery 


Fig. 2.49, cont’d B. Segmental supply of spinal cord. 


■ longitudinally oriented vessels, arising superior to the 
cervical portion of the cord, which descend on the 
surface of the cord; and 

■ feeder arteries that enter the vertebral canal through 
the intervertebral foramina at every level; these feeder 
vessels, or segmental spinal arteries, arise predomi¬ 
nantly from the vertebral and deep cervical arteries in 
the neck, the posterior intercostal arteries in the thorax, 
and the lumbar arteries in the abdomen. 

After entering an intervertebral foramen, the segmental 
spinal arteries give rise to anterior and posterior radicu¬ 
lar arteries (Fig. 2.49). This occurs at every vertebral 
level. The radicular arteries follow, and supply, the anterior 
and posterior roots. At various vertebral levels, the seg¬ 
mental spinal arteries also give off segmental medul¬ 
lary arteries (Fig. 2.49). These vessels pass directly to the 
longitudinally oriented vessels, reinforcing these. 


The longitudinal vessels consist of; 

■ a single anterior spinal artery, which originates 
within the cranial cavity as the union of two vessels that 
arise from the vertebral arteries—the resulting single 
anterior spinal artery passes inferiorly, approximately 
parallel to the anterior median fissure, along the surface 
of the spinal cord; and 

■ two posterior spinal arteries, which also originate in 
the cranial cavity, usually arising directly from a termi¬ 
nal branch of each vertebral artery (the posterior infe¬ 
rior cerebellar artery)—the right and left posterior 
spinal arteries descend along the spinal cord, each as 
two branches that bracket the posterolateral sulcus and 
the connection of posterior roots with the spinal cord. 

The anterior and posterior spinal arteries are reinforced 
along their length by eight to ten segmental medullary 101 

























Back 


arteries (Fig. 2.49). The largest of these is the arteria 
radicularis magna or the artery of Adamkiewicz 

(Fig. 2.49). This vessel arises in the lower thoracic or upper 
lumbar region, usually on the left side, and reinforces the 
arterial supply to the lower portion of the spinal cord, 
including the lumbar enlargement. 

Veins 

Veins that drain the spinal cord form a number of longitu¬ 
dinal channels (Fig. 2.50): 

■ Two pairs of veins on each side bracket the connections 
of the posterior and anterior roots to the cord. 


■ One midline channel parallels the anterior median 
fissure. 

■ One midline channel passes along the posterior median 
sulcus. 

These longitudinal channels drain into an extensive 
internal vertebral plexus in the extradural (epidural) 
space of the vertebral canal, which then drains into seg- 
mentally arranged vessels that connect with major sys¬ 
temic veins, such as the azygos system in the thorax. The 
internal vertebral plexus also communicates with intracra¬ 
nial veins. 



Posterior spinal vein 


Anterior spinal vein 


Internal vertebral plexus 


Extradural fat 


Dura mater 


Fig. 2.50 Veins that drain the spinal cord. 
















Regional anatomy • Spinal Cord 


2 


Meninges 
Spinal dura mater 

The spinal dura mater is the outermost meningeal mem¬ 
brane and is separated from the bones forming the verte¬ 
bral canal by an extradural space (Fig. 2.51). Superiorly, it 
is continuous with the inner meningeal layer of cranial 
dura mater at the foramen magnum of the skull. Interiorly, 
the dural sac dramatically narrows at the level of the lower 
border of vertebra SII and forms an investing sheath for the 
pial part of the filum terminale of the spinal cord. This 
terminal cord-like extension of dura mater (the dural part 
of the filum terminale) attaches to the posterior surface of 
the vertebral bodies of the coccyx. 

As spinal nerves and their roots pass laterally, they are 
surrounded by tubular sleeves of dura mater, which merge 
with and become part of the outer covering (epineurium) 
of the nerves. 

Arachnoid mater 

The arachnoid mater is a thin delicate membrane 
against, but not adherent to, the deep surface of the dura 


mater (Fig. 2.51). It is separated from the pia mater by the 
subarachnoid space. The arachnoid mater ends at the level 
of vertebra SII (see Fig. 2.47). 

Subarachnoid space 

The subarachnoid space between the arachnoid and pia 
mater contains CSF (Fig. 2.51). The subarachnoid space 
around the spinal cord is continuous at the foramen 
magnum with the subarachnoid space surrounding the 
brain. Interiorly, the subarachnoid space terminates at 
approximately the level of the lower border of vertebra SII 
(see Fig. 2.47). 

Delicate strands of tissue (arachnoid trabeculae) are 
continuous with the arachnoid mater on one side and the 
pia mater on the other; they span the subarachnoid space 
and interconnect the two adjacent membranes. Large 
blood vessels are suspended in the subarachnoid space by 
similar strands of material, which expand over the vessels 
to form a continuous external coat. 

The subarachnoid space extends further interiorly than 
the spinal cord. The spinal cord ends at approximately 
the disc between vertebrae LI and LII, whereas the 



Recurrent meningeal nerves 


Anterior spinal artery 


Subarachnoid space 

Pia mater 


Dura mater 


Posterior spinal artery 


Denticulate ligament 


Fig. 2.51 Meninges. 


103 

















Back 


subarachnoid space extends to approximately the lower 
border of vertebra SII (see Fig. 2.47). The subarachnoid 
space is largest in the region inferior to the terminal end of 
the spinal cord, where it surrounds the cauda equina. As 
a consequence, CSF can be withdrawn from the subarach¬ 
noid space in the lower lumbar region without endanger¬ 
ing the spinal cord. 

Pia mater 

The spinal pia mater is a vascular membrane that firmly 
adheres to the surface of the spinal cord (Fig. 2.51). It 
extends into the anterior median fissure and reflects as 
sleeve-like coatings onto posterior and anterior rootlets 
and roots as they cross the subarachnoid space. As the 
roots exit the space, the sleeve-like coatings reflect onto the 
arachnoid mater. 

On each side of the spinal cord, a longitudinally ori¬ 
ented sheet of pia mater (the denticulate ligament) 
extends laterally from the cord toward the arachnoid and 
dura mater (Fig. 2.51). 

■ Medially, each denticulate ligament is attached to the 
spinal cord in a plane that lies between the origins of the 
posterior and anterior rootlets. 

■ Laterally, each denticulate ligament forms a series of 
triangular extensions along its free border, with the 
apex of each extension being anchored through the 
arachnoid mater to the dura mater. 

The lateral attachments of the denticulate ligaments 
generally occur between the exit points of adjacent poste¬ 
rior and anterior rootlets. The ligaments function to posi¬ 
tion the spinal cord in the center of the subarachnoid 
space. 


Arrangement of structures in 
the vertebral canal 

The vertebral canal is bordered: 

■ anteriorly by the bodies of the vertebrae, intervertebral 
discs, and posterior longitudinal ligament (Fig. 2.52); 

■ laterally, on each side by the pedicles and intervertebral 
foramina; and 

■ posteriorly by the laminae and ligamenta flava, and in 
the median plane the roots of the interspinous liga¬ 
ments and vertebral spinous processes. 

Between the walls of the vertebral canal and the dural 
sac is an extradural space containing a vertebral plexus of 
veins embedded in fatty connective tissue. 

The vertebral spinous processes can be palpated through 
the skin in the midline in thoracic and lumbar regions 
of the back. Between the skin and spinous processes is a 
layer of superficial fascia. In lumbar regions, the adjacent 
spinous processes and the associated laminae on either side 
of the midline do not overlap, resulting in gaps between 
adjacent vertebral arches. 

When carrying out a lumbar puncture (spinal tap), the 
needle passes between adjacent vertebral spinous pro¬ 
cesses, through the supraspinous and interspinous liga¬ 
ments, and enters the extradural space. The needle 
continues through the dura and arachnoid mater and 
enters the subarachnoid space, which contains CSF. 


Regional anatomy • Spinal Cord 



Fig. 2.52 Arrangement of structures in the vertebral canal and the back (lumbar region). 




























Back 


In the clinic 

Lumbar cerebrospinal fluid tap 

A lumbar tap (puncture) is carried out to obtain a sample 
of CSF for examination. In addition, passage of a needle or 
conduit into the subarachnoid space (CSF space) is used 
to inject antibiotics, chemotherapeutic agents, and 
anesthetics. 

The lumbar region is an ideal site to access the 
subarachnoid space because the spinal cord terminates 
around the level of the disc between vertebrae LI and Lll 
in the adult. The subarachnoid space extends to the 
region of the lower border of the Sll vertebra. There is 
therefore a large CSF-filled space containing lumbar and 
sacral nerve roots but no spinal cord. 

Depending on the clinician's preference, the patient is 
placed in the lateral or prone position. A needle is passed 
in the midline in between the spinous processes into the 
extradural space. Further advancement punctures the 
dura and arachnoid mater to enter the subarachnoid 
space. Most needles push the roots away from the tip 
without causing the patient any symptoms. Once the 
needle is in the subarachnoid space, fluid can be 


Spinal nerves 

Each spinal nerve is connected to the spinal cord by poste¬ 
rior and anterior roots (Fig. 2.53): 

■ The posterior root contains the processes of sensory 
neurons carrying information to the CNS—the cell 
bodies of the sensory neurons, which are derived 
embryologically from neural crest cells, are clustered in 
a spinal ganglion at the distal end of the posterior 
root, usually in the intervertebral foramen. 

■ The anterior root contains motor nerve fibers, which 
carry signals away from the CNS—the cell bodies of the 
primary motor neurons are in anterior regions of the 
spinal cord. 

Medially, the posterior and anterior roots divide into 
rootlets, which attach to the spinal cord. 


aspirated. In some situations, it is important to measure 
CSF pressure. 

Local anesthetics can be injected into the extradural 
space or the subarachnoid space to anesthetize the sacral 
and lumbar nerve roots. Such anesthesia is useful for 
operations on the pelvis and the legs, which can then be 
carried out without the need for general anesthesia. When 
procedures are carried out, the patient must be in the 
erect position and not lying on his or her side or in the 
head-down position. If a patient lies on his or her side, the 
anesthesia is likely to be unilateral. If the patient is placed 
in the head-down position, the anesthetic can pass 
cranially and potentially depress respiration. 

In some instances, anesthesiologists choose to carry 
out extradural anesthesia. A needle is placed through 
the skin, supraspinous ligament, interspinous ligament, 
and ligamenta flava into the areolar tissue and fat around 
the dura mater. Anesthetic agent is introduced and 
diffuses around the vertebral canal to anesthetize the 
exiting nerve roots and diffuse into the subarachnoid 
space. 


A spinal segment is the area of the spinal cord that 
gives rise to the posterior and anterior rootlets, which 
will form a single pair of spinal nerves. Laterally, the pos¬ 
terior and anterior roots on each side join to form a spinal 
nerve. 

Each spinal nerve divides, as it emerges from an 
intervertebral foramen, into two major branches: a small 
posterior ramus and a much larger anterior ramus 
(Fig. 2.53): 

■ The posterior rami innervate only intrinsic back 
muscles (the epaxial muscles) and an associated narrow 
strip of skin on the back. 

■ The anterior rami innervate most other skeletal 
muscles (the hypaxial muscles) of the body, including 
those of the limbs and trunk, and most remaining areas 
of the skin, except for certain regions of the head. 


Regional anatomy • Spinal Cord 


2 



Near the point of division into anterior and posterior 
rami, each spinal nerve gives rise to two to four small 
recurrent meningeal (sinuvertebral) nerves (see Fig. 2.51). 
These nerves reenter the intervertebral foramen to supply 
dura, ligaments, intervertebral discs, and blood vessels. 

All major somatic plexuses (cervical, brachial, lumbar, 
and sacral) are formed by anterior rami. 

Because the spinal cord is much shorter than the verte¬ 
bral column, the roots of spinal nerves become longer and 
pass more obliquely from the cervical to coccygeal regions 
of the vertebral canal (Fig. 2.54). 


In adults, the spinal cord terminates at a level approxi¬ 
mately between vertebrae LI and LII, but this can range 
between vertebra TXII and the disc between vertebrae LII 
and LIII. Consequently, posterior and anterior roots forming 
spinal nerves emerging between vertebrae in the lower 
regions of the vertebral column are connected to the spinal 
cord at higher vertebral levels. 

Below the end of the spinal cord, the posterior and ante¬ 
rior roots of lumbar, sacral, and coccygeal nerves pass infe- 
riorly to reach their exit points from the vertebral canal. 
This terminal cluster of roots is the cauda equina. 


107 






















Back 



Fig. 2.54 Course of spinal nerves in the vertebral canal. 





























































Regional anatomy • Spinal Cord 


2 


Nomenclature of spinal nerves 

There are approximately 31 pairs of spinal nerves (Fig. 
2.54), named according to their position with respect to 
associated vertebrae: 

■ eight cervical nerves—Cl to C8, 

■ twelve thoracic nerves—T11 o T12, 

■ five lumbar nerves—LI to L5, 

■ five sacral nerves—SI to S5, 

■ one coccygeal nerve—Co. 

The first cervical nerve (Cl) emerges from the vertebral 
canal between the skull and vertebra Cl (Fig. 2.55). There¬ 
fore cervical nerves C2 to C7 also emerge from the verte¬ 
bral canal above their respective vertebrae. Because there 
are only seven cervical vertebrae, C8 emerges between ver¬ 
tebrae CVII and TI. As a consequence, all remaining spinal 
nerves, beginning with Tl, emerge from the vertebral 
canal below their respective vertebrae. 


In the clinic 
Herpes zoster 

Herpes zoster is the virus that produces chickenpox in 
children. In some patients the virus remains dormant 
in the cells of the spinal ganglia. Under certain 
circumstances, the virus becomes activated and travels 
along the neuronal bundles to the areas supplied by 
that nerve (the dermatome). A rash ensues, which is 
characteristically exquisitely painful. Importantly, this 
typical dermatomal distribution is characteristic of 
this disorder. 



Nerve Cl emerges between 
skull and Cl vertebra 


Nerves C2 to C7 emerge 
superior to pedicles 


Nerve C8 emerges inferior to 
pedicle of CVII vertebra 


Nerves Tl to Co emerge 
inferior to pedicles of 
their respective vertebrae 


Fig. 2.55 Nomenclature of the spinal nerves. 


109 























Back 


In the clinic 

Back pain—alternative explanations 

Back pain is an extremely common condition affecting 
almost all individuals at some stage during their life. It is 
of key clinical importance to identify whether the back 
pain relates to the vertebral column and its attachments 
or relates to other structures. 

The failure to consider other potential structures that 
may produce back pain can lead to significant mortality 
and morbidity. Pain may refer to the back from a number 
of organs situated in the retroperitoneum. Pancreatic pain 
in particular refers to the back and may be associated with 
pancreatic cancer and pancreatitis. Renal pain, which may 
be produced by stones in the renal collecting system or 
renal tumors, also typically refers to the back. More often 
than not this is usually unilateral; however, it can produce 


central posterior back pain. Enlarged lymph nodes in the 
pre- and para-aortic region may produce central posterior 
back pain and may be a sign of solid tumor malignancy, 
infection, or Hodgkin's lymphoma. An enlarging 
abdominal aorta (abdominal aortic aneurysm) may cause 
back pain as it enlarges without rupture. Therefore it is 
critical to think of this structure as a potential cause of 
back pain, because treatment will be lifesaving. Moreover, 
a ruptured abdominal aortic aneurysm may also cause 
acute back pain in the first instance. 

In all patients back pain requires careful assessment 
not only of the vertebral column but also of the chest and 
abdomen in order not to miss other important anatomical 
structures that may produce signs and symptoms 
radiating to the back. 


110 


Surface anatomy • Absence of Lateral Curvatures 


2 


Surface anatomy 

Back surface anatomy 

Surface features of the back are used to locate muscle 
groups for testing peripheral nerves, to determine regions 
of the vertebral column, and to estimate the approximate 
position of the inferior end of the spinal cord. They are also 
used to locate organs that occur posteriorly in the thorax 
and abdomen. 



Fig. 2.56 Normal appearance of the back. A. In women. B. In men. 


Absence of lateral curvatures 

When viewed from behind, the normal vertebral column 
has no lateral curvatures. The vertical skinfurrowbetween 
muscle masses on either side of the midline is straight 
(Fig. 2.56). 



Ill 





Back 


Primary and secondary curvatures 
in the sagittal plane 

When viewed from the side, the normal vertebral column 
has primary curvatures in the thoracic and sacral/ 
coccygeal regions and secondary curvatures in the cervical 
and lumbar regions (Fig. 2.57). The primary curvatures 
are concave anteriorly. The secondary curvatures are 
concave posteriorly. 

Useful nonvertebral skeletal landmarks 

A number of readily palpable bony features provide useful 
landmarks for defining muscles and for locating structures 


associated with the vertebral column. Among these fea¬ 
tures are the external occipital protuberance, the scapula, 
and the iliac crest (Fig. 2.58). 

The external occipital protuberance is palpable in the 
midline at the back of the head just superior to the 
hairline. 

The spine, medial border, and inferior angle of the 
scapula are often visible and are easily palpable. 

The iliac crest is palpable along its entire length, from 
the anterior superior iliac spine at the lower lateral margin 
of the anterior abdominal wall to the posterior superior 
iliac spine near the base of the back. The position of the 
posterior superior iliac spine is often visible as a “sacral 
dimple” just lateral to the midline. 


Thoracic region 

primary curvature 


Sacral/coccygeal region 

primary curvature 



Cervical region 

secondary curvature 


Lumbar region 

secondary curvature 


Fig. 2.57 Normal curvatures of the vertebral column. 






Surface anatomy • Useful Nonvertebral Skeletal Landmarks 


2 


Spine of scapula 


Medial border of scapula 


Inferior angle of scapula 


Fig. 2.58 Back of a woman with major palpable bony landmarks indicated. 



Position of external 
occipital protuberance 


Iliac crest 


Posterior superior iliac spine 


113 












114 


Back 


How to identify specific vertebral 
spinous processes 

Identification of vertebral spinous processes (Fig. 2.59A) 
can be used to differentiate between regions of the verte¬ 
bral column and facilitate visualizing the position of deeper 
structures, such as the inferior ends of the spinal cord and 
subarachnoid space. 


The spinous process of vertebra CII can be identified 
through deep palpation as the most superior bony protu¬ 
berance in the midline inferior to the skull. 

Most of the other spinous processes, except for that of 
vertebra CVII, are not readily palpable because they are 
obscured by soft tissue. 



Position of external 
occipital protuberance 

CII vertebral spinous process 

CVII vertebral spinous process 
Tl vertebral spinous process 


Till vertebral spinous process 


TVII vertebral spinous process 

TXII vertebral spinous process 
LIV vertebral spinous process 
SI I vertebral spinous process 

Tip of coccyx 



B 



CVII vertebral 
spinous process 

Tl vertebral 
spinous process 


Ligamentum nuchae 


Fig. 2.59 The back with the positions of vertebral spinous processes and associated structures indicated. A. In a man. B. In a woman with 
neck flexed. The prominent CVII and Tl vertebral spinous processes are labeled. C. In a woman with neck flexed to accentuate the 
ligamentum nuchae. 


































Surface anatomy • Visualizing the Inferior Ends of the Spinal Cord and Subarachnoid Space 


2 


The spinous process of CVII is usually visible as a promi¬ 
nent eminence in the midline at the base of the neck (Fig. 
2.59B), particularly when the neck is flexed. 

Extending between CVII and the external occipital pro¬ 
tuberance of the skull is the ligamentum nuchae, which is 
readily apparent as a longitudinal ridge when the neck is 
flexed (Fig. 2.59C). 

Inferior to the spinous process of CVII is the spinous 
process of TI, which is also usually visible as a midline 
protuberance. Often it is more prominent than the spinous 
process of CVII (Fig. 2.59A,B). 

The root of the spine of the scapula is at the same level 
as the spinous process of vertebra Till, and the inferior 
angle of the scapula is level with the spinous process of 
vertebraTVII (Fig. 2.59A). 

The spinous process of vertebra TXII is level with the 
midpoint of a vertical line between the inferior angle of the 
scapula and the iliac crest (Fig. 2.59A). 

A horizontal line between the highest point of the iliac 
crest on each side crosses through the spinous process of 
vertebra LIV. The LIII and LV vertebral spinous processes 
can be palpated above and below the LIV spinous process, 
respectively (Fig. 2.59A). 

The sacral dimples that mark the position of the poste¬ 
rior superior iliac spine are level with the SII vertebral 
spinous process (Fig. 2.59A). 


The tip of the coccyx is palpable at the base of the ver¬ 
tebral column between the gluteal masses (Fig. 2.59A). 

The tips of the vertebral spinous processes do not always 
lie in the same horizontal plane as their corresponding 
vertebral bodies. In thoracic regions, the spinous processes 
are long and sharply sloped downward so that their tips lie 
at the level of the vertebral body below. In other words, the 
tip of the Till vertebral spinous process lies at vertebral 
level TIV. 

In lumbar and sacral regions, the spinous processes are 
generally shorter and less sloped than in thoracic regions, 
and their palpable tips more closely reflect the position of 
their corresponding vertebral bodies. As a consequence, 
the palpable end of the spinous process of vertebra LIV lies 
at approximately the LIV vertebral level. 

Visualizing the inferior ends of the spinal 
cord and subarachnoid space 

The spinal cord does not occupy the entire length of 
the vertebral canal. Normally in adults, it terminates 
at the level of the disc between vertebrae LI and LII; 
however, it may end as high as TXII or as low as the 
disc between vertebrae LII and LIII. The subarachnoid 
space ends at approximately the level of vertebra SII 
(Fig. 2.60A). 


Inferior end of spinal cord 
(normally between 
LI and LII vertebra) 


Inferior end of 
subarachnoid space 


A 



Fig. 2.60 Back with the ends of the spinal cord and subarachnoid space indicated. A. In a man. 


TXII vertebral spinous process 


LIV vertebral spinous process 
SII vertebral spinous process 


Tip of coccyx 


Continued 


115 









Back 



LIV vertebral spinous process 


LV vertebral spinous process 


Tip of coccyx 


Needle 


Fig. 2.60, cont’d Back with the ends of the spinal cord and subarachnoid space indicated. B. In a woman lying on her side in a fetal 
position, which accentuates the lumbar vertebral spinous processes and opens the spaces between adjacent vertebral arches. Cerebrospinal 
fluid can be withdrawn from the subarachnoid space in lower lumbar regions without endangering the spinal cord. 


Because the subarachnoid space can be accessed in the 
lower lumbar region without endangering the spinal cord, 
it is important to be able to identify the position of the 
lumbar vertebral spinous processes. The LIV vertebral 
spinous process is level with a horizontal line between the 
highest points on the iliac crests. In the lumbar region, the 
palpable ends of the vertebral spinous processes lie oppo¬ 
site their corresponding vertebral bodies. The subarach¬ 
noid space can be accessed between vertebral levels LIII 
and LIV and between LIV and LV without endangering the 
spinal cord (Fig. 2.60B). The subarachnoid space ends at 
vertebral level SII, which is level with the sacral dimples 
marking the posterior superior iliac spines. 


Identifying major muscles 

A number of intrinsic and extrinsic muscles of the back 
can readily be observed and palpated. The largest of these 

are the trapezius and latissimus dorsi muscles (Fig. 2.61A Fig . 26 i Back muscles. A. in a man with latissimus dorsi, 

and 2.61B). Retracting the scapulae toward the midline trapezius, and erector spinae muscles outlined. 

can accentuate the rhomboid muscles (Fig. 2.61C), which 

lie deep to the trapezius muscle. The erector spinae muscles 

are visible as two longitudinal columns separated by a 

furrow in the midline (Fig. 2.61 A). 






Surface anatomy • Identifying Major Muscles 


2 




Rhomboid minor 


Rhomboid major 


Fig. 2.61, cont’d Back muscles. B. In a man with arms abducted to accentuate the lateral margins of the latissimus dorsi muscles. C. In a 
woman with scapulae externally rotated and forcibly retracted to accentuate the rhomboid muscles. 


117 







Back 



Clinical cases 

Case 1 

SCIATICA VERSUS LUMBAGO 

A 50-year-old woman visited her local family 
practitioner with severe lower back pain radiating 
into her right buttock. 

Low back pain is a common problem in family practice. 

Of the many common causes of low back pain some 
need to be identified early to commence appropriate 
treatment. The common causes include an anular disc 
tear, a disc prolapse that impinges directly on a nerve 


root, spinal stenosis, and mechanical zygapophysial joint 
pain. Overall, the main causes can be distilled into three 
central groups: mechanical back pain, degenerative joint 
disease, and neuronal compression. 

Sciatica and lumbago are not the same. Lumbago is a 
generic term referring to low back pain. Sciatica is a 
name given to pain in the area of distribution of the 
sciatic nerve (L4 to S3), which is commonly felt in the 
buttock and over the posterolateral aspects of the leg. 


Case 2 

CERVICAL SPINAL CORD INJURY 

A 45-year-old man was involved in a serious car 
accident. On examination he had a severe injury to 
the cervical region of his vertebral column with 
damage to the spinal cord. In fact, his breathing 
became erratic and stopped. 

If the cervical spinal cord injury is above the level of 
C5, breathing is likely to stop. The phrenic nerve takes 
origin from C3, C4, and C5 and supplies the diaphragm. 
Breathing may not cease immediately if the lesion is just 
below C5, but does so as the cord becomes edematous 
and damage progresses superiorly. In addition, some 
respiratory and ventilatory exchange may occur by 
using neck muscles plus the sternocleidomastoid and 
trapezius muscles, which are innervated by the 
accessory nerve [XI]. 


The patient was unable to sense or move his upper and 
lower limbs. 

The patient has paralysis of the upper and lower limbs 
and is therefore quadriplegic. If breathing is unaffected, 
the lesion is below the level of C5 or at the level of C5. 
The nerve supply to the upper limbs is via the brachial 
plexus, which begins at the C5 level. The site of the spinal 
cord injury is at or above the C5 level. 

It is important to remember that although the cord has 
been transected in the cervical region, the cord below 
this level is intact. Reflex activity may therefore occur 
below the injury, but communication with the brain 
is lost. 


118 








Clinical cases • Case 4 


2 


Case 3 

PSOAS ABSCESS 

A 25-year-old woman complained of increasing 
lumbar back pain. Over the ensuing weeks she was 
noted to have an enlarging lump in the right groin, 
which was mildly tender to touch. On direct 
questioning, the patient also complained of a 
productive cough with sputum containing mucus and 
blood, and she had a mild temperature. 

The chest radiograph revealed a cavitating apical lung 
mass, which explains the pulmonary history. 

Given the age of the patient a primary lung cancer is 
unlikely. The hemoptysis (coughing up blood in the 
sputum) and the rest of the history suggest the patient 
has a lung infection. Given the chest radiographic 
findings of a cavity in the apex of the lung, a diagnosis 
of tuberculosis (TB) was made. This was confirmed by 
bronchoscopy and aspiration of pus, which was cultured. 

During the patient's pulmonary infection, the tuberculous 
bacillus had spread via the blood to vertebra LI.The bone 
destruction began in the cancellous bone of the vertebral 


body close to the intervertebral discs. This disease 
progressed and eroded into the intervertebral disc, 
which became infected. The disc was destroyed, and the 
infected disc material extruded around the disc anteriorly 
and passed into the psoas muscle sheath. This is not an 
uncommon finding for a tuberculous infection of the 
lumbar portion of the vertebral column. 

As the infection progressed, the pus spread within the 
psoas muscle sheath beneath the inguinal ligament to 
produce a hard mass in the groin. This is a typical finding 
for a psoas abscess. 

Fortunately for the patient, there was no evidence of any 
damage within the vertebral canal. 

The patient underwent a radiologically guided drainage 
of the psoas abscess and was treated for over 6 months 
with a long-term antibiotic regimen. She made an 
excellent recovery with no further symptoms, although 
the cavities within the lungs remain. It healed with 
sclerosis. 


anomaly in blood pressure measurements, which are not 
compatible with the clinical state of the patient. 

It was deduced that the blood pressure measurements 
were obtained in different arms, and both were 
reassessed. 

The blood pressure measurements were true. In the right 
arm the blood pressure measured 120/80 mm Hg and in 
the left arm the blood pressure measured 80/40 mm Hg. 
This would imply a deficiency of blood to the left arm. 

The patient was transferred from the emergency 
department to the CT scanner, and a scan was performed 
that included the chest, abdomen, and pelvis. 


Case 4 

DISSECTING THORACIC ANEURYSM 

A 72-year-old fit and healthy man was brought to 
the emergency department with severe back pain 
beginning at the level of the shoulder blades and 
extending to the midlumbar region. The pain was 
of relatively acute onset and was continuous. The 
patient was able to walk to the gurney as he entered 
the ambulance; however, at the emergency 
department the patient complained of inability 
to use both legs. 

The attending physician examined the back thoroughly 
and found no significant abnormality. He noted that 
there was reduced sensation in both legs, and there 
was virtually no power in extensor or flexor groups. The 
patient was tachycardic, which was believed to be due to 
pain, and the blood pressure obtained in the ambulance 
measured 120/80 mm Hg. It was noted that the patient's 
current blood pressure was 80/40 mm Hg; however, the 
patient did not complain of typical clinical symptoms of 
hypotension. 

On first inspection, it is difficult to "add up" these clinical 
symptoms and signs. In essence we have a progressive 
paraplegia associated with severe back pain and an 


The CT scan demonstrated a dissecting thoracic aortic 
aneurysm. Aortic dissection occurs when the tunica 
intima and part of the tunica media of the wall of the 
aorta become separated from the remainder of the tunica 
media and the tunica adventitia of the aorta wall. This 
produces a false lumen. Blood passes not only in the true 
aortic lumen but also through a small hole into the wall 
ofthe aorta and into the false lumen. It often reenters 
the true aortic lumen inferiorly. This produces two 

(continues) 


119 



Back 



Case 4 (continued) 

channels through which blood may flow. The process 
of the aortic dissection produces considerable pain for 
the patient and is usually of rapid onset. Typically the 
pain is felt between the shoulder blades and radiating 
into the back, and although the pain is not from the 
back musculature or the vertebral column, careful 
consideration of structures other than the back should 
always be sought. 

The difference in the blood pressure between the two 
arms indicates the level at which the dissection has 
begun. The "point of entry" is proximal to the left 
subclavian artery. At this level a small flap has been 
created, which limits the blood flow to the left upper 
limb, giving the low blood pressure recording. The 
brachiocephalic trunk has not been affected by the aortic 
dissection, and hence blood flow remains appropriate to 
the right upper limb. 


The paraplegia was caused by ischemia to the 
spinal cord. 

The blood supply to the spinal cord is from a single 
anterior spinal artery and two posterior spinal arteries. 
These arteries are fed via segmental spinal arteries at 
every vertebral level. There are a number of reinforcing 
arteries (segmental medullary arteries) along the length 
of the spinal cord—the largest of which is the artery of 
Adamkiewicz. This artery of Adamkiewicz, a segmental 
medullary artery, typically arises from the lower thoracic 
or upper lumbar region, and unfortunately during this 
patient's aortic dissection, the origin of this vessel was 
disrupted. This produces acute spinal cord ischemia 
and has produced the paraplegia in the patient. 

Unfortunately, the dissection extended, the aorta 
ruptured, and the patient succumbed. 


Case 5 

SACRAL TUMOR 

A 55-year-old woman came to her physician with 
sensory alteration in the right gluteal (buttock) region 
and in the intergluteal (natal) cleft. Examination also 
demonstrated low-grade weakness of the muscles of 
the foot and subtle weakness of the extensor hallucis 
longus, extensor digitorum longus, and fibularis 
tertius on the right. The patient also complained of 
some mild pain symptoms posteriorly in the right 
gluteal region. 

A lesion was postulated in the left sacrum. 

Pain in the right sacro-iliac region could easily be 
attributed to the sacro-iliac joint, which is often very 
sensitive to pain. The weakness of the intrinsic muscles 
of the foot and the extensor hallucis longus, extensor 
digitorum longus, and fibularis tertius muscles raises the 
possibility of an abnormality affecting the nerves exiting 
the sacrum and possibly the lumbosacral junction. The 
altered sensation around the gluteal region toward the 
anus would also support these anatomical 
localizing features. 

An X-ray was obtained of the pelvis. 

The X-ray appeared on first inspection unremarkable. 
However, the patient underwent further investigation, 


including CT and MRI, which demonstrated a large 
destructive lesion involving the whole of the left sacrum 
extending into the anterior sacral foramina at the SI, 

S2, and S3 levels. Interestingly, plain radiographs of the 
sacrum may often appear normal on first inspection, 
and further imaging should always be sought in patients 
with a suspected sacral abnormality. 

The lesion was expansile and lytic. 

Most bony metastases are typically nonexpansile. They 
may well erode the bone, producing lytic type of lesions, 
or may become very sclerotic (prostate metastases and 
breast metastases). From time to time we see a mixed 
pattern of lytic and sclerotic. 

There are a number of uncommon instances in which 
certain metastases are expansile and lytic. These typically 
occur in renal metastases and may be seen in multiple 
myeloma. The anatomical importance of these specific 
tumors is that they often expand and impinge upon 
other structures. The expansile nature of this patient's 
tumor within the sacrum was the cause for compression 
of the sacral nerve roots, producing her symptoms. 

The patient underwent a course of radiotherapy, had the 
renal tumor excised, and is currently undergoing a course 
of chemoimmunotherapy. 


120 








■ Image Library—illustrations of thoracic anatomy, 
Chapter 3 

■ Self-Assessment—National Board style multiple- 
choice questions, Chapter 3 

■ Short Questions—these are questions requiring 
short responses, Chapter 3 

■ Interactive Surface Anatomy—interactive surface 
animations, Chapter 3 

■ Medical Clinical Case Studies, Chapter 3 
Cardiac tamponade 

Patent ductus arteriosus 
Subclavian steal syndrome 
Sinus of Valsalva aneurysm 
Free Online Anatomy and Embryology 
Self-Study Course 

■ Anatomy modules 4 through 9 

■ Embryology modules 61 through 64 


V ‘ - 

Conceptual overview 

General description 
Functions 

Breathing 

Protection of vital organs 
C ond uit 

arts 

Thoracic wall 

Superior thoracic aperture 
Inferior thoradc aperture 
Diaphragm 
Mediastinum 
Pleural cavities/ 

Relationship to other regions 

Neck 130 
Upper limb 
Abdomen 
Breast 

Key features 

Vertebral level TIV/V 
Venous shunts from left to right 
Segmental neurovascular supply of thoracic 
wall 

Sympathetic system 

Flexible wall and inferior thoracic aperture 
Innervation pf the diaphragm 

Regional anatomy 

ctoral region 
Breast 

Muscles of the pectoral region 
Thoracic wall 

Skeletal framework 
Intercostal spaces 
Diaphragm 

Arterial supply 
Venous drainage 
Innervation 




Movements of the thoracic wall and diaphragm 
during breathing 162 
Pleural cavities 162 
Pleura 163 
Lungs 167 
Mediastinum 180 

Middle mediastinum 180 
Superior mediastinum 210 
Posterior mediastinum 222 
Anterior mediastinum 230 

Surface anatomy 231 

Thorax surface anatomy 231 
How to count ribs 231 


Surface anatomy of the breast in women 232 
Visualizing structures at the TIV/V vertebral 
level 232 

Visualizing structures in the superior 
mediastinum 234 

Visualizing the margins of the heart 235 
Where to listen for heart sounds 236 
Visualizing the pleural cavities and lungs, pleural 
recesses, and lung lobes and fissures 236 
Where to listen for lung sounds 238 

Clinical cases 241 



Conceptual overview • General Description 


3 


Conceptual overview 

GENERAL DESCRIPTION 


The thorax is an irregularly shaped cylinder with a narrow 
opening (superior thoracic aperture) superiorly and a rela¬ 
tively large opening (inferior thoracic aperture) inferiorly 
(Fig. 3.1). The superior thoracic aperture is open, allowing 
continuity with the neck; the inferior thoracic aperture is 
closed by the diaphragm. 

The musculoskeletal wall of the thorax is flexible and 
consists of segmentally arranged vertebrae, ribs, and 
muscles and the sternum. 


The thoracic cavity enclosed by the thoracic wall 
and the diaphragm is subdivided into three major 
compartments: 

■ a left and a right pleural cavity, each surrounding a 
lung, and 

■ the mediastinum. 



Body of sternum 


Ribs 


Manubrium of sternum 


Sternal angle 


Right pleural cavity 


Left pleural cavity 
-Rib I 


Inferior thoracic aperture 


Vertebral column 


Diaphragm 


Xiphoid process 


Superior thoracic aperture 


Mediastinum 


Fig. 3.1 Thoracic wall and cavity. 


123 
























Thorax 



The mediastinum is a thick, flexible soft tissue partition 
oriented longitudinally in a median sagittal position. It 
contains the heart, esophagus, trachea, major nerves, and 
major systemic blood vessels. 

The pleural cavities are completely separated from each 
other by the mediastinum. Therefore, abnormal events in 
one pleural cavity do not necessarily affect the other cavity. 
This also means that the mediastinum can be entered sur¬ 
gically without opening the pleural cavities. 

Another important feature of the pleural cavities is that 
they extend above the level of rib I. The apex of each lung 
actually extends into the root of the neck. As a conse¬ 
quence, abnormal events in the root of the neck can involve 
the adjacent pleura and lung, and events in the adjacent 
pleura and lung can involve the root of the neck. 

FUNCTIONS 

Breathing 

One of the most important functions of the thorax is 
breathing. The thorax not only contains the lungs but also 
provides the machinery necessary—the diaphragm, tho¬ 
racic wall, and ribs—for effectively moving air into and out 
of the lungs. 

Up and down movements of the diaphragm and 
changes in the lateral and anterior dimensions of the 
thoracic wall, caused by movements of the ribs, alter 
the volume of the thoracic cavity and are key elements 
in breathing. 

Protection of vital organs 

The thorax houses and protects the heart, lungs, and great 
vessels. Because of the domed shape of the diaphragm, the 
thoracic wall also offers protection to some important 
abdominal viscera. 

Much of the liver lies under the right dome of the dia¬ 
phragm, and the stomach and spleen lie under the left. The 
posterior aspects of the superior poles of the kidneys lie on 
the diaphragm and are anterior to rib XII, on the right, and 
to ribs XI and XII, on the left. 


Conduit 

The mediastinum acts as a conduit for structures that pass 
completely through the thorax from one body region to 
another and for structures that connect organs in the 
thorax to other body regions. 

The esophagus, vagus nerves, and thoracic duct pass 
through the mediastinum as they course between the 
abdomen and neck. 

The phrenic nerves, which originate in the neck, also 
pass through the mediastinum to penetrate and supply the 
diaphragm. 

Other structures such as the trachea, thoracic 
aorta, and superior vena cava course within the mediasti¬ 
num en route to and from major visceral organs in the 
thorax. 

COMPONENT PARTS 
Thoracic wall 

The thoracic wall consists of skeletal elements and 
muscles (Fig. 3.1): 

■ Posteriorly, it is made up of twelve thoracic vertebrae 
and their intervening intervertebral discs; 

■ Laterally, the wall is formed by ribs (twelve on each side) 
and three layers of flat muscles, which span the inter¬ 
costal spaces between adjacent ribs, move the ribs, and 
provide support for the intercostal spaces; 

■ Anteriorly, the wall is made up of the sternum, which 
consists of the manubrium of sternum, body of sternum, 
and xiphoid process. 

The manubrium of sternum, angled posteriorly on the 
body of sternum at the manubriosternal joint, forms the 
sternal angle, which is a major surface landmark used by 
clinicians in performing physical examinations of the 
thorax. 

The anterior (distal) end of each rib is composed of 
costal cartilage, which contributes to the mobility and elas¬ 
ticity of the wall. 


124 




Conceptual overview • Component Ports 


3 


All ribs articulate with thoracic vertebrae posteriorly. 
Most ribs (from rib II to IX) have three articulations with 
the vertebral column. The head of each rib articulates 
with the body of its own vertebra and with the body of the 
vertebra above (Fig. 3.2). As these ribs curve posteriorly, 
each also articulates with the transverse process of its 
vertebra. 

Anteriorly, the costal cartilages of ribs I to VII articulate 
with the sternum. 

The costal cartilages of ribs VIII to X articulate with the 
inferior margins of the costal cartilages above them. Ribs 


XI and XII are called floating ribs because they do not artic¬ 
ulate with other ribs, costal cartilages, or the sternum. 
Their costal cartilages are small, only covering their tips. 

The skeletal framework of the thoracic wall provides 
extensive attachment sites for muscles of the neck, 
abdomen, back, and upper limbs. 

A number of these muscles attach to ribs and function 
as accessory respiratory muscles; some of them also stabi¬ 
lize the position of the first and last ribs. 



Intervertebral disc 


Inferior articular 
process 


Vertebral body 


Inferior costal facet 


Costal facet of 
transverse process 


Rib V 


Sternum 


Superior articular process 


Superior costal facet 


Costal cartilage 


Fig. 3.2 Joints between ribs and vertebrae. 


125 












Thorax 


Superior thoracic aperture 

Completely surrounded by skeletal elements, the superior 
thoracic aperture consists of the body of vertebra TI pos¬ 
teriorly, the medial margin of rib I on each side, and the 
manubrium anteriorly. 

The superior margin of the manubrium is in approxi¬ 
mately the same horizontal plane as the intervertebral disc 
between vertebrae TII and Till. 

The first ribs slope interiorly from their posterior articu¬ 
lation with vertebra TI to their anterior attachment to 
the manubrium. Consequently, the plane of the superior 
thoracic aperture is at an oblique angle, facing somewhat 
anteriorly. 

At the superior thoracic aperture, the superior aspects 
of the pleural cavities, which surround the lungs, lie on 
either side of the entrance to the mediastinum (Fig. 3.3). 

Structures that pass between the upper limb and thorax 
pass over rib I and the superior part of the pleural cavity 
as they enter and leave the mediastinum. Structures that 
pass between the neck and head and the thorax pass more 
vertically through the superior thoracic aperture. 


Inferior thoracic aperture 

The inferior thoracic aperture is large and expandable. 
Bone, cartilage, and ligaments form its margin (Fig. 3.4A). 

The inferior thoracic aperture is closed by the dia¬ 
phragm, and structures passing between the abdomen and 
thorax pierce or pass posteriorly to the diaphragm. 

Skeletal elements of the inferior thoracic aperture are: 

■ the body of vertebra TXII posteriorly, 

■ rib XII and the distal end of rib XI posterolaterally, 

■ the distal cartilaginous ends of ribs VII to X, which unite 
to form the costal margin anterolaterally, and 

■ the xiphoid process anteriorly. 

The joint between the costal margin and sternum lies 
roughly in the same horizontal plane as the intervertebral 
disc between vertebrae TIX and TX. In other words, the 
posterior margin of the inferior thoracic aperture is infe¬ 
rior to the anterior margin. 

When viewed anteriorly, the inferior thoracic aperture 
is tilted superiorly. 



Trachea 


Internal 
jugular vein 


Subclavian 
artery and vein 


Rib II 


Common carotid artery 
Vertebra TI 

Superior thoracic aperture 
Rib I 


Apex of right lung 


Manubrium 
of sternum 


126 


Fig. 3.3 Superior thoracic aperture. 






















Conceptual overview • Component Ports 


3 


Xiphoid process 

Inferior thoracic 
aperture 

Distal cartilaginous 
ends of ribs VII to X; 
costal margins 

Rib XI 
Rib XII 

Vertebra TXII 
A 



Central 

tendon 


Left dome 


Esophageal 

hiatus 

Aortic 

hiatus 


Fig. 3.4 A. Inferior thoracic aperture. B. Diaphragm. 


Diaphragm 

The musculotendinous diaphragm seals the inferior tho¬ 
racic aperture (Fig. 3.4B). 

Generally, muscle fibers of the diaphragm arise radially, 
from the margins of the inferior thoracic aperture, and 
converge into a large central tendon. 

Because of the oblique angle of the inferior thoracic 
aperture, the posterior attachment of the diaphragm is 
inferior to the anterior attachment. 


The diaphragm is not fiat; rather, it “balloons” superi¬ 
orly, on both the right and left sides, to form domes. The 
right dome is higher than the left, reaching as far as rib V. 

As the diaphragm contracts, the height of the domes 
decreases and the volume of the thorax increases. 

The esophagus and inferior vena cava penetrate the dia¬ 
phragm; the aorta passes posterior to the diaphragm. 


127 




















Thorax 


Mediastinum 

The mediastinum is a thick midline partition that extends 
from the sternum anteriorly to the thoracic vertebrae pos¬ 
teriorly, and from the superior thoracic aperture to the infe¬ 
rior thoracic aperture. 

A horizontal plane passing through the sternal angle 
and the intervertebral disc between vertebrae TIV and TV 
separates the mediastinum into superior and inferior parts 
(Fig. 3.5). The inferior part is further subdivided by the 
pericardium, which encloses the pericardial cavity sur¬ 
rounding the heart. The pericardium and heart constitute 
the middle mediastinum. 

The anterior mediastinum lies between the sternum and 
the pericardium; the posterior mediastinum lies between 
the pericardium and thoracic vertebrae. 

Pleural cavities 

The two pleural cavities are situated on either side of the 
mediastinum (Fig. 3.6). 


Each pleural cavity is completely lined by a mesothe- 
lial membrane called the pleura. 

During development, the lungs grow out of the medias¬ 
tinum, becoming surrounded by the pleural cavities. As a 
result, the outer surface of each organ is covered by pleura. 

Each lung remains attached to the mediastinum by a 
root formed by the airway, pulmonary blood vessels, lym¬ 
phatic tissues, and nerves. 

The pleura lining the walls of the cavity is the parietal 
pleura, whereas that reflected from the mediastinum at the 
roots and onto the surfaces of the lungs is the visceral 
pleura. Only a potential space normally exists between the 
visceral pleura covering lung and the parietal pleura lining 
the wall of the thoracic cavity. 

The lung does not completely fill the potential space of 
the pleural cavity, resulting in recesses, which do not 
contain lung and are important for accommodating 
changes in lung volume during breathing. The costodia¬ 
phragmatic recess, which is the largest and clinically most 
important recess, lies inferiorly between the thoracic wall 
and diaphragm. 



Superior mediastinum — 


Inferior mediastinum — 


Sternal angle 


Rib I 


Diaphragm 


Anterior mediastinum 


Middle mediastinum 


Posterior mediastinum 


128 


Fig. 3.5 Subdivisions of the mediastinum. 
















Conceptual overview • Component Ports 


3 



Parietal pleura 

Visceral pleura 

Right pleural cavity 


Mediastinum 


Apex of right lung 


Trachea 


Costodiaphragmatic 

recess 


Diaphragm 


Right main bronchus 


Left pleural cavity 
surrounding left lung 


Fig. 3.6 Pleural cavities. 


129 

















Thorax 


RELATIONSHIPJTO OTHER REGIONS 

Neck 

The superior thoracic aperture opens directly into the root 
of the neck (Fig. 3.7). 

The superior aspect of each pleural cavity extends 
approximately 2-3 cm above rib I and the costal cartilage 
into the neck. Between these pleural extensions, major vis¬ 
ceral structures pass between the neck and superior medi¬ 
astinum. In the midline, the trachea lies immediately 
anterior to the esophagus. Major blood vessels and nerves 
pass in and out of the thorax at the superior thoracic aper¬ 
ture anteriorly and laterally to these structures. 


Upper limb 

An axillary inlet, or gateway to the upper limb, lies on 
each side of the superior thoracic aperture. These two axil¬ 
lary inlets and the superior thoracic aperture communi¬ 
cate superiorly with the root of the neck (Fig. 3.7). 

Each axillary inlet is formed by: 

■ the superior margin of the scapula posteriorly, 

■ the clavicle anteriorly, and 

■ the lateral margin of rib I medially. 

The apex of each triangular inlet is directed laterally 
and is formed by the medial margin of the coracoid process, 


Superior thoracic aperture Rib I 



Esophagus - 
Brachial plexus 


Scapula 

Axillary inlet 


Subclavian 
artery and vein 


Trachea 

Clavicle 


Coracoid 

process 


130 


Fig. 3.7 Superior thoracic aperture and axillary inlet. 


which extends anteriorly from the superior margin of the 
scapula. 

The base of the axillary inlet’s triangular opening is the 
lateral margin of rib I. 

Large blood vessels passing between the axillary inlet 
and superior thoracic aperture do so by passing over rib I. 

Proximal parts of the brachial plexus also pass 
between the neck and upper limb by passing through the 
axillary inlet. 


Abdomen 

The diaphragm separates the thorax from the abdomen. 

Structures that pass between the thorax and abdomen 

either penetrate the diaphragm or pass posteriorly to it 

(Fig. 3.8): 

■ The inferior vena cava pierces the central tendon of 
the diaphragm to enter the right side of the mediasti¬ 
num near vertebral level TVIII. 

■ The esophagus penetrates the muscular part of the 
diaphragm to leave the mediastinum and enter the 
abdomen just to the left of the midline at vertebral 
level TX. 


Inferior vena cava 


Esophagus 


Caval opening 
(vertebral level TVIII) 


Aorta 

Central tendon 
of diaphragm 



Aortic hiatus 
(vertebral level TXII) 


Esophageal hiatus 
(vertebral level TX) 


Fig. 3.8 Major structures passing between abdomen and thorax. 



























Conceptual overview • Relationship to Other Regions 


3 


■ The aorta passes posteriorly to the diaphragm at the 
midline at vertebral level TXII. 

■ Numerous other structures that pass between the 
thorax and abdomen pass through or posterior to the 
diaphragm. 

Breast 

The breasts, consisting of secretory glands, superficial 
fascia, and overlying skin, are in the pectoral region on 
each side of the anterior thoracic wall (Fig. 3.9). 

Vessels, lymphatics, and nerves associated with the 
breast are as follows: 

■ Branches from the internal thoracic arteries and veins 
perforate the anterior chest wall on each side of the 


sternum to supply anterior aspects of the thoracic wall. 
Those branches associated mainly with the second to 
fourth intercostal spaces also supply the anteromedial 
parts of each breast. 

■ Lymphatic vessels from the medial part of the breast 
accompany the perforating arteries and drain into 
the parasternal nodes on the deep surface of the tho¬ 
racic wall. 

■ Vessels and lymphatics associated with lateral parts of 
the breast emerge from or drain into the axillary region 
of the upper limb. 

■ Lateral and anterior branches of the fourth to sixth 
intercostal nerves carry general sensation from the skin 
of the breast. 



Axillary 
lymph nodes 


Axillary process 


Fourth thoracic 
intercostal nerve 


Lymphatic vessel 



Internal 

thoracic artery Pectoralis major 


Second, third, and fourth anterior 
perforating branches of internal 
thoracic artery 


Parasternal 
lymph nodes 


Lactiferous 

sinuses 


Lactiferous 
ducts 

Secretory glands 


Deep (pectoral) fascia 


A 


B 


Fig. 3.9 Right breast. 


131 












Thorax 


KEY FEATURES 
Vertebral level TIV/V 

When working with patients, physicians use vertebral 
levels to determine the position of important anatomical 
structures within body regions. 

The horizontal plane passing through the disc that 
separates thoracic vertebrae TIV and TV is one of the most 
significant planes in the body (Fig. 3.10) because it: 

■ passes through the sternal angle anteriorly, marking 
the position of the anterior articulation of the costal 
cartilage of rib II with the sternum. The sternal angle 
is used to find the position of rib II as a reference for 
counting ribs (because of the overlying clavicle, rib I is 
not palpable); 

■ separates the superior mediastinum from the inferior 
mediastinum and marks the position of the superior 
limit of the pericardium; 

■ marks where the arch of the aorta begins and ends; 

■ passes through the site where the superior vena cava 
penetrates the pericardium to enter the heart; 

■ is the level at which the trachea bifurcates into right and 
left main bronchi; and 

■ marks the superior limit of the pulmonary trunk. 


Venous shunts from left to right 

The right atrium is the chamber of the heart that receives 
deoxygenated blood returning from the body. It lies on 
the right side of the midline, and the two major veins, 
the superior and inferior venae cavae, that drain into it are 
also located on the right side of the body. This means that, 
to get to the right side of the body, all blood coming from 
the left side has to cross the midline. This left-to-right 
shunting is carried out by a number of important and, in 
some cases, very large veins, several of which are in the 
thorax (Fig. 3.11). 

In adults, the left brachiocephalic vein crosses the 
midline immediately posterior to the manubrium and 
delivers blood from the left side of the head and neck, the 
left upper limb, and part of the left thoracic wall into the 
superior vena cava. 

The hemiazygos and accessory hemiazygos veins drain 
posterior and lateral parts of the left thoracic wall, pass 
immediately anterior to the bodies of thoracic vertebrae, 
and flow into the azygos vein on the right side, which ulti¬ 
mately connects with the superior vena cava. 



Inferior 

mediastinum 


Superior mediastinum 
Aortic arch 


Sternal angle 


T rachea 


Rib II 


TIV 


Fig. 3.10 Vertebral level TIV/V. 












Conceptual overview • Key Features 


3 


Superior vena cava 


Right atrium 


Azygos vein 


Inferior vena cava 



Left internal 
jugular vein 


Hemiazygos vein 


Left 

brachiocephalic 

vein 

_Intercostal vein 


Accessory 
hemiazygos vein 


Fig. 3.11 Left-to-right venous shunts. 


133 

















Thorax 


Segmental neurovascular supply 
of thoracic wall 

The arrangement of vessels and nerves that supply the 
thoracic wall reflects the segmental organization of the 
wall. Arteries to the wall arise from two sources: 

■ the thoracic aorta, which is in the posterior mediasti¬ 
num, and 


■ a pair of vessels, the internal thoracic arteries, which 
run along the deep aspect of the anterior thoracic wall 
on either side of the sternum. 

Posterior and anterior intercostal vessels branch seg- 
mentally from these arteries and pass laterally around 
the wall, mainly along the inferior margin of each rib 
(Fig. 3.12A). Running with these vessels are intercostal 
nerves (the anterior rami of thoracic spinal nerves), which 
innervate the wall, related parietal pleura, and associated 



Right subclavian artery 


Left common carotid artery 


— Internal thoracic arteries 


Arch of aorta 


Intercostal nerve 


Anterior 

cutaneous branch 


Lateral 
cutaneous branch 


Posterior 
intercostal artery 


Anterior 

intercostal artery 


Fig. 3.12 A. Segmental neurovascular supply of thoracic wall. 
















Conceptual overview • Key Features 


3 




Fig. 3.12, cont’d B. Anterior view of thoracic dermatomes associated with thoracic spinal nerves. C. Lateral view of dermatomes associated 
with thoracic spinal nerves. 


skin. The position of these nerves and vessels relative to the 
ribs must be considered when passing objects, such as 
chest tubes, through the thoracic wall. 

Dermatomes of the thorax generally reflect the segmen¬ 
tal organization of the thoracic spinal nerves (Fig. 3.12B). 
The exception occurs, anteriorly and superiorly, with the 
first thoracic dermatome, which is located mostly in the 
upper limb, and not on the trunk. 


The anterosuperior region of the trunk receives 
branches from the anterior ramus of C4 via supraclavicu¬ 
lar branches of the cervical plexus. 

The highest thoracic dermatome on the anterior 
chest wall is T2, which also extends into the upper limb. 
In the midline, skin over the xiphoid process is innervated 
by T6. 

Dermatomes ofT7toT12 follow the contour of the ribs 
onto the anterior abdominal wall (Fig. 3.12C). 


135 











































Thorax 


Sympathetic system 

All preganglionic nerve fibers of the sympathetic system 
are carried out of the spinal cord in spinal nerves T1 to L2 
(Fig. 3.13). This means that sympathetic fibers found any¬ 
where in the body ultimately emerge from the spinal cord 
as components of these spinal nerves. Preganglionic sym¬ 
pathetic fibers destined for the head are carried out of the 
spinal cord in spinal nerve Tl. 

Flexible wall and inferior thoracic aperture 

The thoracic wall is expandable because most ribs articu¬ 
late with other components of the wall by true joints that 


allow movement, and because of the shape and orientation 
of the ribs (Fig. 3.14). 

A rib’s posterior attachment is superior to its anterior 
attachment. Therefore, when a rib is elevated, it moves the 
anterior thoracic wall forward relative to the posterior wall, 
which is fixed. In addition, the middle part of each rib is 
inferior to its two ends, so that when this region of the rib 
is elevated, it expands the thoracic wall laterally. Finally, 
because the diaphragm is muscular, it changes the volume 
of the thorax in the vertical direction. 

Changes in the anterior, lateral, and vertical dimensions 
of the thoracic cavity are important for breathing. 


Paravertebral 
sympathetic trunk 


Spinal cord 


Spinal nerve 



Fig. 3.13 Sympathetic trunks. 


136 

































Conceptual overview • Key Features 


3 



Elevation of lateral aspect 
of ribs in inspiration 


Sternum moves forward 
in inspiration because of 
rib elevation 


Diaphragm descends to 
increase thoracic capacity 
in inspiration 


Fig. 3.14 Flexible thoracic wall and inferior thoracic aperture. 


137 



















Thorax 


Innervation of the diaphragm 

The diaphragm is innervated by two phrenic nerves that 
originate, one on each side, as branches of the cervical 
plexus in the neck (Fig. 3.15). They arise from the anterior 
rami of cervical nerves C3, C4, and C5, with the major 
contribution coming from C4. 

The phrenic nerves pass vertically through the neck, 
the superior thoracic aperture, and the mediastinum 
to supply motor innervation to the entire diaphragm, 
including the crura (muscular extensions that attach the 


diaphragm to the upper lumbar vertebrae). In the medias¬ 
tinum, the phrenic nerves pass anteriorly to the roots of 
the lungs. 

The tissues that initially give rise to the diaphragm are 
in an anterior position on the embryological disc before the 
head fold develops, which explains the cervical origin of 
the nerves that innervate the diaphragm. In other words, 
the tissue that gives rise to the diaphragm originates supe¬ 
rior to the ultimate location of the diaphragm. 

Spinal cord injuries below the level of the origin of the 
phrenic nerve do not affect movement of the diaphragm. 


Right phrenic 


Pericardial branch 
of phrenic nerve 


Diaphragm 



Pericardium 


nerve 


Left phrenic nerve 


138 


Fig. 3.15 Innervation of the diaphragm. 





















Regional anatomy • Pectoral Region 


3 


Regional anatomy 

The cylindrical thorax consists of: 

■ a wall, 

■ two pleural cavities, 

■ the lungs, and 

■ the mediastinum. 

The thorax houses the heart and lungs, acts as a conduit 
for structures passing between the neck and the abdomen, 
and plays a principal role in breathing. In addition, the 
thoracic wall protects the heart and lungs and provides 
support for the upper limbs. Muscles anchored to the ante¬ 
rior thoracic wall provide some of this support, and together 
with their associated connective tissues, nerves, and 
vessels, and the overlying skin and superficial fascia, define 
the pectoral region. 

PECTORAL REGION 

The pectoral region is external to the anterior thoracic wall 
and anchors the upper limb to the trunk. It consists of: 

■ a superficial compartment containing skin, superficial 
fascia, and breasts; and 

■ a deep compartment containing muscles and associated 
structures. 

Nerves, vessels, and lymphatics in the superficial com¬ 
partment emerge from the thoracic wall, the axilla, and 
the neck. 

Breast 

The breasts consist of mammary glands and associated 
skin and connective tissues. The mammary glands 
are modified sweat glands in the superficial fascia anterior 
to the pectoral muscles and the anterior thoracic wall 
(Fig. 3.16). 

The mammary glands consist of a series of ducts and 
associated secretory lobules. These converge to form 15 to 
20 lactiferous ducts, which open independently onto the 
nipple. The nipple is surrounded by a circular pigmented 
area of skin termed the areola. 

A well-developed, connective tissue stroma surrounds 
the ducts and lobules of the mammary gland. In certain 
regions, this condenses to form well-defined ligaments, the 
suspensory ligaments of breast, which are continuous 
with the dermis of the skin and support the breast. 


Carcinoma of the breast creates tension on these liga¬ 
ments, causing pitting of the skin. 

In nonlactating women, the predominant component 
of the breasts is fat, while glandular tissue is more abun¬ 
dant in lactating women. 

The breast lies on deep fascia related to the pectoralis 
major muscle and other surrounding muscles. A layer of 
loose connective tissue (the retromammary space) sepa¬ 
rates the breast from the deep fascia and provides some 
degree of movement over underlying structures. 

The base, or attached surface, of each breast extends 
vertically from ribs II to VI, and transversely from the 
sternum to as far laterally as the midaxillary line. 

Arterial supply 

The breast is related to the thoracic wall and to structures 
associated with the upper limb; therefore, vascular supply 
and drainage can occur by multiple routes (Fig. 3.16): 

■ laterally, vessels from the axillary artery—superior tho¬ 
racic, thoraco-acromial, lateral thoracic, and subscapu¬ 
lar arteries; 

■ medially, branches from the internal thoracic artery; 

■ the second to fourth intercostal arteries via branches 
that perforate the thoracic wall and overlying muscle. 

Venous drainage 

Veins draining the breast parallel the arteries and ulti¬ 
mately drain into the axillary, internal thoracic, and inter¬ 
costal veins. 

Innervation 

Innervation of the breast is via anterior and lateral cutane¬ 
ous branches of the second to sixth intercostal nerves. The 
nipple is innervated by the fourth intercostal nerve. 

Lymphatic drainage 

Lymphatic drainage of the breast is as follows: 

■ Approximately 75% is via lymphatic vessels that drain 
laterally and superiorly into axillary nodes (Fig. 3.16). 

■ Most of the remaining drainage is into parasternal 
nodes deep to the anterior thoracic wall and associated 
with the internal thoracic artery. 

■ Some drainage may occur via lymphatic vessels that 
follow the lateral branches of posterior intercostal arter¬ 
ies and connect with intercostal nodes situated near the 
heads and necks of ribs. 


139 




Thorax 


Internal thoracic artery 



Areola 


Secretory 

lobules 


Pectoral branch of 
thoraco-acromial artery 


Pectoralis major muscle 


Apical axillary nodes 


Central axillary nodes 

Lateral thoracic artery 

Lateral axillary nodes 

Pectoral axillary nodes 

Axillary process 


Lymphatic and venous drainage 
passes from lateral and superior 
part of the breast into axilla 


Secretory lobules 

Suspensory ligaments 
Lactiferous ducts 

Lactiferous sinuses 

Retromammary space 

Parasternal nodes 


Mammary branches of 
internal thoracic artery 

Lymphatic and venous 
drainage passes from medial part 
of the breast parasternally 


Some lymphatic and venous drainage 
may pass from inferior part of the 
breast into the abdomen 


Fig. 3.16 Breasts. 


140 













Regional anatomy • Pectoral Region 


3 


Axillary nodes drain into the subclavian trunks, para¬ 
sternal nodes drain into the bronchomediastinal trunks, 
and intercostal nodes drain either into the thoracic duct or 
into the bronchomediastinal trunks. 


Breast in men 

The breast in men is rudimentary and consists only of 
small ducts, often composed of cords of cells, that normally 
do not extend beyond the areola. Breast cancer can occur 
in men. 


In the clinic 

Axillary tail of breast 

It is important for clinicians to remember when 
evaluating the breast for pathology that the upper 
lateral region of the breast can project around the 
lateral margin of the pectoralis major muscle and into 
the axilla. This axillary process (axillary tail) may 
perforate deep fascia and extend as far superiorly as the 
apex of the axilla. 


In the clinic 

Breast cancer 

Breast cancer is one of the most common malignancies in 
women. It develops in the cells of the acini, lactiferous 
ducts, and lobules of the breast. Tumor growth and 
spread depends on the exact cellular site of origin of the 
cancer. These factors affect the response to surgery, 
chemotherapy, and radiotherapy. Breast tumors spread 
via the lymphatics and veins, or by direct invasion. 

When a patient has a lump in the breast, a diagnosis of 
breast cancer is confirmed by a biopsy and histological 
evaluation. Once confirmed, the clinician must attempt to 
stage the tumor. 

Staging the tumor means defining the: 

■ size of the primary tumor, 

■ exact site of the primary tumor, 

■ number and sites of lymph node spread, and 

■ organs to which the tumor may have spread. 

Computed tomography (CT) scanning of the body may 
be carried out to look for any spread to the lungs 
(pulmonary metastases), liver (hepatic metastases), or 
bone (bony metastases). 

Further imaging may include bone scanning using 
radioactive isotopes, which are avidly taken up by the 
tumor metastases in bone. 


Lymph drainage of the breast is complex. Lymph 
vessels pass to axillary, supraclavicular, and parasternal 
nodes and may even pass to abdominal lymph nodes, as 
well as to the opposite breast. Containment of nodal 
metastatic breast cancer is therefore potentially difficult 
because it can spread through many lymph node groups. 

Subcutaneous lymphatic obstruction and tumor 
growth pull on connective tissue ligaments in the breast, 
resulting in the appearance of an orange peel texture 
(peau d'orange) on the surface of the breast. Further 
subcutaneous spread can induce a rare manifestation of 
breast cancer that produces a hard, woody texture to the 
skin (cancer en cuirasse). 

A mastectomy (surgical removal of the breast) involves 
excision of the breast tissue to the pectoralis major muscle 
and fascia. Within the axilla the breast tissue must be 
removed from the medial axillary wall. Closely applied to 
the medial axillary wall is the long thoracic nerve. Damage 
to this nerve can result in paralysis of the serratus anterior 
muscle, producing a characteristic "winged" scapula. It is 
also possible to damage the nerve to the latissimus dorsi 
muscle, and this may affect extension, medial rotation, 
and adduction of the humerus. 


141 



Thorax 


142 


Muscles of the pectoral region 

Each pectoral region contains the pectoralis major, pecto- 
ralis minor, and subclavius muscles (Fig. 3.17 and Table 
3.1). All originate from the anterior thoracic wall and 
insert into bones of the upper limb. 


Pectoralis major 

The pectoralis major muscle is the largest and most 
superficial of the pectoral region muscles. It directly under¬ 
lies the breast and is separated from it by deep fascia and 
the loose connective tissue of the retromammary space. 


Subclavius 

, Lateral pectoral nerve 



Pectoralis minor 

Medial pectoral nerve 
Lateral thoracic artery 


Clavipectoral fascia 


Pectoralis major 


Thoraco-acromial artery 


Fig. 3.17 Muscles and fascia of the pectoral region. 


Table 3.1 Muscles of the pectoral region 


Muscle 

Origin 

Insertion 

Innervation 

Function 

Pectoralis major 

Medial half of clavicle and 
anterior surface of sternum, 
first seven costal cartilages, 
aponeurosis of external 
oblique 

Lateral lip of intertubercular 
sulcus of humerus 

Medial and lateral 
pectoral nerves 

Adduction, medial rotation, 
and flexion of the humerus at 
the shoulder joint 

Subclavius 

Rib 1 at junction between rib 
and costal cartilage 

Groove on inferior surface 
of middle third of clavicle 

Nerve to subclavius 

Pulls clavicle medially to 
stabilize sternoclavicular joint; 
depresses tip of shoulder 

Pectoralis minor 

Anterior surfaces of the third, 
fourth, and fifth ribs, and 

Coracoid process of scapula 

Medial pectoral nerves 

Depresses tip of shoulder; 
protracts scapula 


deep fascia overlying the 
related intercostal spaces 

















Regional anatomy • Thoracic Wall 


3 


The pectoralis major has a broad origin that includes 
the anterior surfaces of the medial half of the clavicle, the 
sternum, and related costal cartilages. The muscle fibers 
converge to form a flat tendon, which inserts into the 
lateral lip of the intertubercular sulcus of the humerus. 

The pectoralis major adducts, flexes, and medially 
rotates the arm. 

Subdavius and pectoralis minor muscles 

The subdavius and pectoralis minor muscles underlie 
the pectoralis major: 

■ The subdavius is small and passes laterally from the 
anterior and medial part of rib I to the inferior surface 
of the clavicle. 

■ The pectoralis minor passes from the anterior surfaces 
of ribs III to V to the coracoid process of the scapula. 

Both the subdavius and pectoralis minor pull the tip of 
the shoulder inferiorly. 

A continuous layer of deep fascia, the clavipectoral 
fascia, encloses the subdavius and pectoralis minor and 
attaches to the clavicle above and to the floor of the axilla 
below. 

The muscles of the pectoral region form the anterior 
wall of the axilla, a region between the upper limb and the 
neck through which all major structures pass. Nerves, 
vessels, and lymphatics that pass between the pectoral 
region and the axilla pass through the clavipectoral fascia 
between the subdavius and pectoralis minor or pass under 
the inferior margins of the pectoralis major and minor. 


THORACIC WALL 

The thoracic wall is segmental in design and composed of 
skeletal elements and muscles. It extends between: 

■ the superior thoracic aperture, bordered by vertebra TI, 
rib I, and the manubrium of the sternum; and 

■ the inferior thoracic aperture, bordered by vertebra 
TXII, rib XII, the end of rib XI, the costal margin, and 
the xiphoid process of the sternum. 

Skeletal framework 

The skeletal elements of the thoracic wall consist of 
the thoracic vertebrae, intervertebral discs, ribs, and 
sternum. 

Thoracic vertebrae 

There are twelve thoracic vertebrae, each of which is 
characterized by articulations with ribs. 

Typical thoracic vertebra 

A typical thoracic vertebra has a heart-shaped vertebral 
body, with roughly equal dimensions in the transverse 
and anteroposterior directions, and a long spinous process 
(Fig. 3.18). The vertebral foramen is generally circular 
and the laminae are broad and overlap with those of the 
vertebra below. The superior articular processes are 
flat, with their articular surfaces facing almost directly pos¬ 
teriorly, while the inferior articular processes project 
from the laminae and their articular facets face anteriorly. 


Anterior 




Superior articular process 


Superior demifacet 


Inferior articular process 


Demifacets for articulation 
with head of ribs 


Vertebral body 


Facet for articulation 
with tubercle of rib 


Superior 


Vertebral 

foramen 


Pedicle 


Posterior 


Anterior 


Spinous process 


Lamina 


Facet for articulation 
with tubercle of rib 


Transverse process 


Posterior 


Superior view 


Superolateral view 


Fig. 3.18 Typical thoracic vertebra. 


143 





















Thorax 


The transverse processes are club shaped and project 
posterolaterally. 

Articulation with ribs 

A typical thoracic vertebra has three sites on each side for 
articulation with ribs. 

■ Two demifacets (i.e., partial facets) are located on the 
superior and inferior aspects of the body for articulation 
with corresponding sites on the heads of adjacent ribs. 
The superior costal facet articulates with part of the 
head of its own rib, and the inferior costal facet artic¬ 
ulates with part of the head of the rib below. 

■ An oval facet (transverse costal facet) at the end of 
the transverse process articulates with the tubercle of 
its own rib. 

Not all vertebrae articulate with ribs in the same fashion 
(Fig. 3.19): 

■ The superior costal facets o n the body o f vertebra TI are 
complete and articulate with a single facet on the head 
of its own rib—in other words, the head of rib I does not 
articulate with vertebra CVII. 

■ Similarly, vertebra TX (and often TIX) articulates only 
with its own ribs and therefore lacks inferior demifacets 
on the body. 

■ Vertebrae TXI and TXII articulate only with the heads 
of their own ribs—they lack transverse costal facets and 
have only a single complete facet on each side of their 
bodies. 

Ribs 

There are twelve pairs of ribs, each terminating anteriorly 
in a costal cartilage (Fig. 3.20). 

Although all ribs articulate with the vertebral column, 
only the costal cartilages of the upper seven ribs, known 
as true ribs, articulate directly with the sternum. The 
remaining five pairs of ribs are false ribs: 

■ The costal cartilages of ribs VIII to X articulate anteri¬ 
orly with the costal cartilages of the ribs above. 

■ Ribs XI and XII have no anterior connection with 
other ribs or with the sternum and are often called 

floating ribs. 

A typical rib consists of a curved shaft with anterior and 
posterior ends (Fig. 3.21). The anterior end is continuous 
with its costal cartilage. The posterior end articulates with 
the vertebral column and is characterized by a head, neck, 
and tubercle. 





Fig. 3.19 Atypical thoracic vertebrae. 


144 










Regional anatomy • Thoracic Wall 


3 



True ribs I—VII 


Intercostal space 

Costal cartilage 


False ribs VIII—XII 


Floating ribs 
Costal margin 


Fig. 3.20 Ribs. 



A 



Fig. 3.21 A typical rib. A. Anterior view. B. Posterior view of 
proximal end of rib. 


145 































Thorax 


The head is somewhat expanded and typically presents 
two articular surfaces separated by a crest. The smaller 
superior surface articulates with the inferior costal facet on 
the body of the vertebra above, whereas the larger inferior 
facet articulates with the superior costal facet of its own 
vertebra. 

The neck is a short flat region of bone that separates 
the head from the tubercle. 

The tubercle projects posteriorly from the junction of 
the neck with the shaft and consists of two regions, an 
articular part and a nonarticular part: 

■ The articular part is medial and has an oval facet for 
articulation with a corresponding facet on the trans¬ 
verse process of the associated vertebra. 

■ The raised nonarticular part is roughened by ligament 
attachments. 

The shaft is generally thin and flat with internal and 
external surfaces. 

The superior margin is smooth and rounded, whereas 
the inferior margin is sharp. The shaft bends forward just 
laterally to the tubercle at a site termed the angle. It also 
has a gentle twist around its longitudinal axis so that the 
external surface of the anterior part of the shaft faces 
somewhat superiorly relative to the posterior part. The 
inferior margin of the internal surface is marked by a 
distinct costal groove. 

Distinct features of upper and lower ribs 

The upper and lower ribs have distinct features (Fig. 3.22). 

Rib I 

Rib I is flat in the horizontal plane and has broad superior 
and inferior surfaces. From its articulation with vertebra 
TI, it slopes interiorly to its attachment to the manubrium 
of the sternum. The head articulates only with the body of 
vertebra TI and therefore has only one articular surface. 
Like other ribs, the tubercle has a facet for articulation with 
the transverse process. The superior surface of the rib is 
characterized by a distinct tubercle, the scalene tubercle, 
which separates two smooth grooves that cross the rib 
approximately midway along the shaft. The anterior groove 
is caused by the subclavian vein, and the posterior groove 
is caused by the subclavian artery. Anterior and posterior 


Rib I 



Rib XII 



to these grooves, the shaft is roughened by muscle and liga¬ 
ment attachments. 

Rib II 

Rib II, like rib I, is flat but twice as long. It articulates with 
the vertebral column in a way typical of most ribs. 

Rib X 

The head of rib X has a single facet for articulation with 
its own vertebra. 

Ribs XI and XII 

Ribs XI and XII articulate only with the bodies of their 
own vertebrae and have no tubercles or necks. Both ribs 
are short, have little curve, and are pointed anteriorly. 


146 









Regional anatomy • Thoracic Wall 


3 


Sternum 

The adult sternum consists of three major elements: the 
broad and superiorly positioned manubrium of the 
sternum, the narrow and longitudinally oriented body of 
the sternum, and the small and inferiorly positioned 
xiphoid process (Fig. 3.23). 

Manubrium of the sternum 

The manubrium of the sternum forms part of the bony 
framework of the neck and the thorax. 

The superior surface of the manubrium is expanded 
laterally and bears a distinct and palpable notch, the 
jugular notch (suprasternal notch), in the midline. 
On either side of this notch is a large oval fossa for articula¬ 
tion with the clavicle. Immediately inferior to this fossa, on 
each lateral surface of the manubrium, is a facet for the 
attachment of the first costal cartilage. At the lower end of 
the lateral border is a demifacet for articulation with the 


upper half of the anterior end of the second costal 
cartilage. 

Body of the sternum 

The body of the sternum is flat. 

The anterior surface of the body of the sternum is often 
marked by transverse ridges that represent lines of fusion 
between the segmental elements called sternebrae, from 
which this part of the sternum arises embryologically. 

The lateral margins of the body of the sternum have 
articular facets for costal cartilages. Superiorly, each lateral 
margin has a demifacet for articulation with the inferior 
aspect of the second costal cartilage. Inferior to this demi¬ 
facet are four facets for articulation with the costal carti¬ 
lages of ribs III to VI. 

At the inferior end of the body of the sternum is a demi¬ 
facet for articulation with the upper demifacet on the 
seventh costal cartilage. The inferior end of the body of the 
sternum is attached to the xiphoid process. 



Fig. 3.23 Sternum. 


Xiphoid 

process 


147 











Thorax 


Xiphoid process 

The xiphoid process is the smallest part of the sternum. 
Its shape is variable: it may be wide, thin, pointed, bifid, 
curved, or perforated. It begins as a cartilaginous struc¬ 
ture, which becomes ossified in the adult. On each side of 
its upper lateral margin is a demifacet for articulation with 
the inferior end of the seventh costal cartilage. 

Joints 

Costovertebral joints 

A typical rib articulates with: 

■ the bodies of adjacent vertebrae, forming a joint with 
the head of the rib; and 

■ the transverse process of its related vertebra, forming a 

costotransverse joint (Fig. 3.24). 


Together, the costovertebral joints and related ligaments 
allow the necks of the ribs either to rotate around their 
longitudinal axes, which occurs mainly in the upper ribs, 
or to ascend and descend relative to the vertebral column, 
which occurs mainly in the lower ribs. The combined 
movements of all of the ribs on the vertebral column are 
essential for altering the volume of the thoracic cavity 
during breathing. 

Joint with head of rib 

The two facets on the head of the rib articulate with the 
superior facet on the body of its own vertebra and with the 
inferior facet on the body of the vertebra above. This joint 
is divided into two synovial compartments by an intra- 
articular ligament, which attaches the crest to the adjacent 
intervertebral disc and separates the two articular surfaces 
on the head of the rib. The two synovial compartments and 
the intervening ligament are surrounded by a single joint 




Vertebra 


Disc 

Intra-articular 

ligament 

Vertebra 


Joint with vertebral body 


Lateral 

costotransverse 

ligament 


Costotransverse joint 


Superolateral view 


Superior view 


Fig. 3.24 Costovertebral joints. 


Superior 

costotransverse ligament 


Joint capsule 


Costotransverse 

ligament 


cavities 


148 
























Regional anatomy • Thoracic Wall 


3 


capsule attached to the outer margins of the combined 
articular surfaces of the head and vertebral column. 

Costotransverse joints 

Costotransverse joints are synovial joints between 
the tubercle of a rib and the transverse process of the 
related vertebra (Fig. 3.24). The capsule surrounding 
each joint is thin. The joint is stabilized by two strong extra- 
capsular ligaments that span the space between the trans¬ 
verse process and the rib on the medial and lateral sides of 
the joint: 

■ The costotransverse ligament is medial to the joint 
and attaches the neck of the rib to the transverse 
process. 


■ The lateral costotransverse ligament is lateral to the 
joint and attaches the tip of the transverse process to the 
roughened nonarticular part of the tubercle of the rib. 

A third ligament, the superior costotransverse liga¬ 
ment, attaches the superior surface of the neck of the rib 
to the transverse process of the vertebra above. 

Slight gliding movements occur at the costotransverse 
joints. 

Sternocostal joints 

The sternocostal joints are joints between the upper seven 
costal cartilages and the sternum (Fig. 3.25). 

The joint between rib I and the manubrium is not 
synovial and consists of a fibrocartilaginous connection 



Sternal angle 


Manubriosternal joint 
(symphysis) 


Fibrocartilaginous joint 


Synovial joint 
(two compartments) 


Synovial joint 


Fig. 3.25 Sternocostal joints. 


149 




























Thorax 


between the manubrium and the costal cartilage. The 
second to seventh joints are synovial and have thin cap¬ 
sules reinforced by surrounding sternocostal ligaments. 

The joint between the second costal cartilage and the 
sternum is divided into two compartments by an intra- 
articular ligament. This ligament attaches the second 
costal cartilage to the junction of the manubrium and the 
body of the sternum. 

Interchondral joints 

Interchondral joints occur between the costal cartilages of 
adjacent ribs (Fig. 3.25), mainly between the costal carti¬ 
lages of ribs VII to X, but may also involve the costal carti¬ 
lages of ribs V and VI. 

Interchondral joints provide indirect anchorage to the 
sternum and contribute to the formation of a smooth infe¬ 
rior costal margin. They are usually synovial, and the thin 
fibrous capsules are reinforced by interchondral ligaments. 

Manubriosternal and xiphisternal joints 

The joints between the manubrium and the body of the 
sternum and between the body of the sternum and the 
xiphoid process are usually symphyses (Fig. 3.25). Only 
slight angular movements occur between the manubrium 
and the body of the sternum during respiration. The joint 
between the body of the sternum and the xiphoid process 
often becomes ossified with age. 

A clinically useful feature of the manubriosternal joint 
is that it can be palpated easily. This is because the manu¬ 
brium normally angles posteriorly on the body of the 
sternum, forming a raised feature referred to as the sternal 
angle. This elevation marks the site of articulation of rib II 
with the sternum. Rib I is not palpable, because it lies infe¬ 
rior to the clavicle and is embedded in tissues at the base 
of the neck. Therefore, rib II is used as a reference for 
counting ribs and can be felt immediately lateral to the 
sternal angle. 

In addition, the sternal angle lies on a horizontal plane 
that passes through the intervertebral disc between verte¬ 
brae TIV and TV (see Fig. 3.10). This plane separates the 
superior mediastinum from the inferior mediastinum and 
marks the superior border of the pericardium. The plane 
also passes through the end of the ascending aorta and the 
beginning of the arch of the aorta, the end of the arch of 
the aorta and the beginning of the thoracic aorta, and the 
bifurcation of the trachea, and just superior to the pulmo¬ 
nary trunk (see Fig. 3.79 and 3.86). 

Intercostal spaces 

Intercostal spaces lie between adjacent ribs and are filled 
150 by intercostal muscles (Fig. 3.26). 


Intercostal nerves and associated major arteries and 
veins lie in the costal groove along the inferior margin of 
the superior rib and pass in the plane between the inner 
two layers of muscles. 

In each space, the vein is the most superior structure 
and is therefore highest in the costal groove. The artery 
is inferior to the vein, and the nerve is inferior to the 
artery and often not protected by the groove. Therefore, 
the nerve is the structure most at risk when objects 
perforate the upper aspect of an intercostal space. 
Small collateral branches of the major intercostal nerves 
and vessels are often present superior to the inferior 
rib below. 

Deep to the intercostal spaces and ribs, and separating 
these structures from the underlying pleura, is a layer of 
loose connective tissue, called endothoracic fascia, 
which contains variable amounts of fat. 

Superficial to the spaces are deep fascia, superficial 
fascia, and skin. Muscles associated with the upper limbs 
and back overlie the spaces. 


In the clinic 
Cervical ribs 

Cervical ribs are present in approximately 1% of the 
population. 

A cervical rib is an accessory rib articulating with 
vertebra CVII; the anterior end attaches to the superior 
border of the anterior aspect of rib I. 

Plain radiographs may demonstrate cervical ribs as 
small horn-like structures (see Fig. 3.106). 

It is often not appreciated by clinicians that a fibrous 
band commonly extends from the anterior tip of the 
small cervical ribs to rib I, producing a "cervical band" 
that is not visualized on radiography. In patients with 
cervical ribs and cervical bands, structures that normally 
pass over rib I (see Fig. 3.7) are elevated by, and pass 
over, the cervical rib and band. 

Clinically, "thoracic outlet syndrome" is used to 
describe symptoms resulting from abnormal 
compression of the brachial plexus of nerves as it passes 
over the first rib and through the axillary inlet into the 
upper limb. The anterior ramus of T1 passes superiorly 
out of the superior thoracic aperture to join and 
become part of the brachial plexus. The cervical band 
from a cervical rib is one cause of thoracic outlet 
syndrome by putting upward stresses on the lower 
parts of the brachial plexus as they pass over the 
first rib. 


Regional anatomy • Thoracic Wall 


3 



Anterior cutaneous 
branch of 
intercostal nerve 


Collateral branches of 
intercostal nerve and vessels 


Endothoracic fascia 


Anterior intercostal artery and vein 


Anterior perforating 
branches of 
intercostal vessels 


Posterior ramus of spinal nerve 


Posterior intercostal artery and vein 


Serratus anterior muscle 

External intercostal muscle 
Internal intercostal muscle 
Innermost intercostal muscle 

Skin 

Superficial fascia 


Lateral branches of- 

intercostal nerve 
and vessels 


Internal thoracic artery 
and vein 


Lung 

Pleural cavity 
Visceral pleura 
Parietal pleura 


Intercostal vein 
Intercostal artery 
Intercostal nerve 


]-Collateral branches 


Fig. 3.26 Intercostal space. A. Anterolateral view. B. Details of an intercostal space and relationships. 


151 















































Thorax 




Aorta 


Internal intercostal 
muscle 


Posterior intercostal artery 


Internal thoracic artery 
Anterior cutaneous branch 


Anterior perforating branch 


External intercostal 
muscle 


Anterior intercostal artery 


Innermost intercostal 
muscle 


Anterior ramus 
(intercostal nerve) 

Posterior ramus 


Spinal nerve 


Lateral cutaneous 
branch 


Lateral cutaneous 
branch 


Fig. 3.26, cont’d Intercostal space. C. Transverse section. 


In the clinic 

Collection of sternal bone marrow 

The subcutaneous position of the sternum makes it 
possible to place a needle through the hard outer 
cortex into the internal (or medullary) cavity containing 
bone marrow. Once the needle is in this position, bone 
marrow can be aspirated. Evaluation of this material 
under the microscope helps clinicians diagnose certain 
blood diseases such as leukemia. 


In the clinic 

Rib fractures 

Single rib fractures are of little consequence, though 
extremely painful. 

After severe trauma, ribs may be broken in two or 
more places. If enough ribs are broken, a loose segment 
of chest wall, a flail segment (flail chest), is produced. 
When the patient takes a deep inspiration, the flail 
segment moves in the opposite direction to the chest 
wall, preventing full lung expansion and creating a 
paradoxically moving segment. If a large enough 
segment of chest wall is affected, ventilation may be 
impaired and assisted ventilation may be required until 
the ribs have healed. 


Muscles 

Muscles of the thoracic wall include those that fill and 
support the intercostal spaces, those that pass between the 
sternum and the ribs, and those that cross several ribs 
between costal attachments (Table 3.2). 

The muscles of the thoracic wall, together with 
muscles between the vertebrae and ribs posteriorly (i.e., 
the levatores costarum and serratus posterior supe¬ 
rior and serratus posterior inferior muscles) alter 
the position of the ribs and sternum and so change the 
thoracic volume during breathing. They also reinforce the 
thoracic wall. 

Intercostal muscles 

The intercostal muscles are three flat muscles found 
in each intercostal space that pass between adjacent ribs 
(Fig. 3.27). Individual muscles in this group are named 
according to their positions: 

■ The external intercostal muscles are the most 
superficial. 

■ The internal intercostal muscles are sandwiched 
between the external and innermost muscles. 

■ The innermost intercostal muscles are the deepest of the 
three muscles. 


152 






















Regional anatomy • Thoracic Wall 


3 


Table 3.2 Muscles of the thoracic wall 


Muscle 

Superior attachment 

Inferior attachment 

Innervation 

Function 

External intercostal 

Inferior margin of rib above 

Superior margin of rib below 

Intercostal nerves; 
T1-T11 

Most active during 
inspiration; supports 
intercostal space; moves 
ribs superiorly 

Internal intercostal 

Lateral edge of costal groove 
of rib above 

Superior margin of rib below 
deep to the attachment of 
the related external 
intercostal 

Intercostal nerves; 
T1-T11 

Most active during 
expiration; supports 
intercostal space; moves 
ribs interiorly 

Innermost intercostal 

Medial edge of costal groove 
of rib above 

Internal aspect of superior 
margin of rib below 

Intercostal nerves; 
T1-T11 

Acts with internal 
intercostal muscles 

Subcostales 

Internal surface (near angle) 
of lower ribs 

Internal surface of second or 
third rib below 

Related intercostal 

nerves 

May depress ribs 

Transversus thoracis 

Inferior margins and internal 
surfaces of costal cartilages of 
second to sixth ribs 

Inferior aspect of deep 
surface of body of sternum, 
xiphoid process, and costal 
cartilages of ribs IV—VII 

Related intercostal 

nerves 

Depresses costal 
cartilages 



Fig. 3.27 Intercostal muscles. 


153 

























Thorax 


The intercostal muscles are innervated by the related 
intercostal nerves. As a group, the intercostal muscles 
provide structural support for the intercostal spaces during 
breathing. They can also move the ribs. 

External intercostal muscles 

The eleven pairs of external intercostal muscles extend 
from the inferior margins (lateral edges of costal grooves) 
of the ribs above to the superior margins of the ribs below. 
When the thoracic wall is viewed from a lateral position, 
the muscle fibers pass obliquely anteroinferiorly (Fig. 3.27). 
The muscles extend around the thoracic wall from the 
regions of the tubercles of the ribs to the costal cartilages, 
where each layer continues as a thin connective tissue 
aponeurosis termed the external intercostal mem¬ 
brane. The external intercostal muscles are most active in 
inspiration. 

Internal intercostal muscles 

The eleven pairs of internal intercostal muscles pass 
between the most inferior lateral edge of the costal grooves 
of the ribs above, to the superior margins of the ribs below. 
They extend from parasternal regions, where the muscles 
course between adjacent costal cartilages, to the angle of 
the ribs posteriorly (Fig. 3.27). This layer continues medi¬ 
ally toward the vertebral column, in each intercostal space, 
as the internal intercostal membrane. The muscle 
fibers pass in the opposite direction to those of the external 
intercostal muscles. When the thoracic wall is viewed from 
a lateral position, the muscle fibers pass obliquely postero- 
inferiorly. The internal intercostal muscles are most active 
during expiration. 

Innermost intercostal muscles 

The innermost intercostal muscles are the least distinct 
of the intercostal muscles, and the fibers have the same 
orientation as the internal intercostals (Fig. 3.27). These 
muscles are most evident in the lateral thoracic wall. They 
extend between the inner surfaces of adjacent ribs from the 
medial edge of the costal groove to the deep surface of the 
rib below. Importantly, the neurovascular bundles associ¬ 
ated with the intercostal spaces pass around the thoracic 
wall in the costal grooves in a plane between the innermost 
and internal intercostal muscles. 



Subcostal muscles 
A 



Fig. 3.28 A. Subcostal muscles. B. Transversus thoracis muscles. 


Subcostales 

The subcostales are in the same plane as the innermost 
intercostals, span multiple ribs, and are more numerous in 
lower regions of the posterior thoracic wall (Fig. 3.28A). 
They extend from the internal surfaces of one rib to the 
internal surface of the second (next) or third rib below. 
154 Their fibers parallel the course of the internal intercostal 


muscles and extend from the angle of the ribs to more 
medial positions on the ribs below. 

Transversus thoracis muscles 

The transversus thoracis muscles are found on the 
deep surface of the anterior thoracic wall (Fig. 3.28B) and 
in the same plane as the innermost intercostals. 














Regional anatomy • Thoracic Wall 


3 


The transversus thoracis muscles originate from the 
posterior aspect of the xiphoid process, the inferior part of 
the body of the sternum, and the adjacent costal cartilages 
of the lower true ribs. They pass superiorly and laterally to 
insert into the lower borders of the costal cartilages of ribs 
III to VI. They most likely pull these latter elements 
inferiorly. 

The transversus thoracis muscles lie deep to the internal 
thoracic vessels and secure these vessels to the wall. 

Arterial supply 

Vessels that supply the thoracic wall consist mainly of 
posterior and anterior intercostal arteries, which pass 
around the wall between adjacent ribs in intercostal spaces 


(Fig. 3.29). These arteries originate from the aorta and 
internal thoracic arteries, which in turn arise from the 
subclavian arteries in the root of the neck. Together, the 
intercostal arteries form a basket-like pattern of vascular 
supply around the thoracic wall. 

Posterior intercostal arteries 

Posterior intercostal arteries originate from vessels 
associated with the posterior thoracic wall. The upper two 
posterior intercostal arteries on each side are derived from 
the supreme intercostal artery, which descends into 
the thorax as a branch of the costocervical trunk in the 
neck. The costocervical trunk is a posterior branch of 
the subclavian artery (Fig. 3.29). 



Supreme intercostal 
Costocervical trunk 
Subclavian artery 


Anterior intercostal artery 


Aorta 


Musculophrenic artery 


Superior epigastric artery 


Collateral branch of posterior 
intercostal artery 


Anterior perforating 
branches 


Posterior intercostal artery 


Internal thoracic artery 


Fig. 3.29 Arteries of the thoracic wall. 


155 










Thorax 


The remaining nine pairs of posterior intercostal arter¬ 
ies arise from the posterior surface of the thoracic aorta. 
Because the aorta is on the left side of the vertebral column, 
those posterior intercostal vessels passing to the right 
side of the thoracic wall cross the midline anterior to the 
bodies of the vertebrae and therefore are longer than the 
corresponding vessels on the left. 

In addition to having numerous branches that 
supply various components of the wall, the posterior inter¬ 
costal arteries have branches that accompany lateral cuta¬ 
neous branches of the intercostal nerves to superficial 
regions. 

Anterior intercostal arteries 

The anterior intercostal arteries originate directly or 
indirectly as lateral branches from the internal thoracic 
arteries (Fig. 3.29). 

Each internal thoracic artery arises as a major 
branch of the subclavian artery in the neck. It passes ante¬ 
riorly over the cervical dome of the pleura and descends 
vertically through the superior thoracic aperture and 
along the deep aspect of the anterior thoracic wall. On 
each side, the internal thoracic artery lies posterior to the 
costal cartilages of the upper six ribs and about 1 cm lateral 
to the sternum. At approximately the level of the sixth 
intercostal space, it divides into two terminal branches: 

■ the superior epigastric artery, which continues inte¬ 
riorly into the anterior abdominal wall (Fig. 3.29); 

■ the musculophrenic artery, which passes along the 
costal margin, goes through the diaphragm, and ends 
near the last intercostal space. 

Anterior intercostal arteries that supply the upper six 
intercostal spaces arise as lateral branches from the 


internal thoracic artery, whereas those supplying the lower 
spaces arise from the musculophrenic artery. 

In each intercostal space, the anterior intercostal arter¬ 
ies usually have two branches: 

■ One passes below the margin of the upper rib. 

■ The other passes above the margin of the lower rib and 

meets a collateral branch of the posterior intercostal 

artery. 

The distributions of the anterior and posterior intercos¬ 
tal vessels overlap and can develop anastomotic connec¬ 
tions. The anterior inter costal arteries are generally smaller 
than the posterior vessels. 

In addition to anterior intercostal arteries and a number 
of other branches, the internal thoracic arteries give rise 
to perforating branches that pass directly forward between 
the costal cartilages to supply structures external to the 
thoracic wall. These vessels travel with the anterior cutane¬ 
ous branches of the intercostal nerves. 

Venous drainage 

Venous drainage from the thoracic wall generally parallels 
the pattern of arterial supply (Fig. 3.30). 

Centrally, the intercostal veins ultimately drain into 
the azygos system of veins or into internal thoracic 
veins, which connect with the brachiocephalic veins in 
the neck. 

Often the upper posterior intercostal veins on the 
left side come together and form the left superior 
intercostal vein, which empties into the left brachioce¬ 
phalic vein. 

Similarly, the upper posterior intercostal veins on the 
right side may come together and form the right superior 
intercostal vein, which empties into the azygos vein. 


156 


Regional anatomy • Thoracic Wall 


3 



Right brachiocephalic vein 

Right superior intercostal vein 

Posterior intercostal vein 

Azygos vein 


Left superior intercostal vein 


Left brachiocephalic vein 


Accessory hemiazygos vein 


Anterior intercostal vein 


Hemiazygos vein 


Internal thoracic vein 


Anterior perforating 
branches 


Fig. 3.30 Veins of the thoracic wall. 


157 
















Thorax 


Lymphatic drainage 

Lymphatic vessels of the thoracic wall drain mainly into 
lymph nodes associated with the internal thoracic arteries 
(parasternal nodes), with the heads and necks of ribs 
(intercostal nodes), and with the diaphragm (diaphrag¬ 
matic nodes) (Fig. 3.31). Diaphragmatic nodes are poste¬ 
rior to the xiphoid and at sites where the phrenic nerves 
penetrate the diaphragm. They also occur in regions where 
the diaphragm is attached to the vertebral column. 

Parasternal nodes drain into bronchomediastinal 
trunks. Intercostal nodes in the upper thorax also drain 
into bronchomediastinal trunks, whereas intercostal nodes 
in the lower thorax drain into the thoracic duct. 


Nodes associated with the diaphragm interconnect 
with parasternal, prevertebral, and juxta-esophageal 
nodes, brachiocephalic nodes (anterior to the brachio¬ 
cephalic veins in the superior mediastinum), and lateral 
aortic/lumbar nodes (in the abdomen). 

Superficial regions of the thoracic wall drain mainly 
into axillary lymph nodes in the axilla or parasternal 
nodes. 

Innervation 

Intercostal nerves 

Innervation of the thoracic wall is mainly by the intercos¬ 
tal nerves, which are the anterior rami of spinal nerves 


Thoracic duct 



Lateral aortic nodes 


Right bronchomediastinal trunk 
Brachiocephalic nodes 


Right parasternal 
lymphatic vessel 


Intercostal nodes 


Thoracic duct 


Parasternal nodes 


Diaphragmatic nodes 


Diaphragm 

Cisterna chyli 


Right jugular trunk 


Right subclavian trunk 


Left jugular trunk 
Left subclavian trunk 


Left bronchomediastinal trunk 


Left parasternal 
lymphatic vessel 


Fig. 3.31 Major lymphatic vessels and nodes of the thoracic wall. 





















Regional anatomy • Thoracic Wall 


3 


T1 to Til and lie in the intercostal spaces between adja¬ 
cent ribs. The anterior ramus of spinal nerve T12 (the sub¬ 
costal nerve) is inferior to rib XII (Fig. 3.32). 

A typical intercostal nerve passes laterally around the 
thoracic wall in an intercostal space. The largest of the 
branches is the lateral cutaneous branch, which 
pierces the lateral thoracic wall and divides into an ante¬ 
rior branch and a posterior branch that innervate the over- 
lying skin. 

The intercostal nerves end as anterior cutaneous 
branches, which emerge either parasternally, between 
adjacent costal cartilages, or laterally to the midline, on the 
anterior abdominal wall, to supply the skin. 


In addition to these major branches, small collateral 
branches can be found in the intercostal space running 
along the superior border of the lower rib. 

In the thorax, the intercostal nerves carry: 

■ somatic motor innervation to the muscles of the tho¬ 
racic wall (intercostal, subcostal, and transversus tho¬ 
racis muscles), 

■ somatic sensory innervation from the skin and parietal 
pleura, and 

■ postganglionic sympathetic fibers to the periphery. 


Posterior ramus Spinal cord 



Lateral branch 


Anterior cutaneous 
branch 


- Medial branch 


Posterior branch 


Lateral cutaneous 
branch 


Anterior branch 


Small collateral branch 


Fig. 332 Intercostal nerves. 


159 

















Thorax 


Sensory innervation of the skin overlying the upper 
thoracic wall is supplied by cutaneous branches (supracla¬ 
vicular nerves), which descend from the cervical plexus in 
the neck. 

In addition to innervating the thoracic wall, intercostal 
nerves innervate other regions: 

■ The anterior ramus of T1 contributes to the brachial 
plexus. 

■ The lateral cutaneous branch of the second intercostal 
nerve (the intercostobrachial nerve) contributes to 
cutaneous innervation of the medial surface of the 
upper arm. 

■ The lower intercostal nerves supply the muscles, skin, 
and peritoneum of the abdominal wall. 


In the clinic 

Thoracostomy (chest) tube insertion 

Insertion of a chest tube is a commonly performed 
procedure and is indicated to relieve air or fluid trapped 
in the thorax between the lung and the chest wall 
(pleural cavity). This procedure is done for 
pneumothorax, hemothorax, hemopneumothorax, 
malignant pleural effusion empyema, hydrothorax, and 
chylothorax, and also after thoracic surgery. 

The position of the thoracostomy tube should be 
between the anterior axillary and midaxillary anatomical 
lines from anterior to posterior and either the fourth or 
fifth intercostal space from cephalad to caudad.The 
position of the ribs in this region should be clearly 
marked. Anesthetic should be applied to the superior 
border of the rib and the inferior aspect of the 
intercostal space, including one rib and space above 
and one rib and space below. The neurovascular bundle 
runs in the neurovascular plane, which lies in the 
superior aspect of the intercostal space O'ust below the 
rib); hence, the reason for positioning the tube on the 
superior border of a rib (i.e., at the lowest position in 
the intercostal space). 


In the clinic 

Surgical access to the chest 

A surgical access is potentially more challenging in the 
chest given the rigid nature of the thoracic cage. 
Moreover, access is also dependent upon the organ that 
is operated upon and its relationships to 
subdiaphragmatic structures and structures in the neck. 

A standard incision site would include a median 
sternotomy to obtain access to the heart, including the 
coronary arteries and the cardiac valves. A left lateral 
thoracotomy or a right lateral thoracotomy is an incision 
through an intercostal space to access the lungs and 
the mediastinal structures. 

Minimally invasive thoracic surgery (video-assisted 
thoracic surgery [VATS]) involves making small (1-cm) 
incisions in the intercostal spaces, placing a small 
camera on a telescope, and manipulating other 
instruments through additional small incisions. A 
number of procedures can be performed in this 
manner, including lobectomy, lung biopsy, and 
esophagectomy. 


In the clinic 

Intercostal nerve block 

Local anesthesia of intercostal nerves produces 
excellent analgesia in patients with chest trauma and 
those patients requiring anesthesia for a thoracotomy, 
mastectomy, or upper abdominal surgical procedures. 

The intercostal nerves are situated inferior to the 
rib borders in the neurovascular bundle. Each 
neurovascular bundle is situated deep to the external 
and internal intercostal muscle groups. 

The nerve block may be undertaken using a "blind" 
technique or under direct imaging guidance. 

The patient is placed in the appropriate position 
to access the rib. Typically, under ultrasound guidance, 
a needle may be advanced into the region of the 
subcostal groove, followed by an injection with local 
anesthesia. Depending on the type of local anesthetic, 
analgesia may be short- or long-acting. 

Given the position of the neurovascular bundle and 
the subcostal groove, complications may include 
puncture of the parietal pleura and an ensuing 
pneumothorax. Bleeding may also occur if the artery 
or vein is damaged during the procedure. 


160 


Regional anatomy • Diaphragm 


3 


DIAPHRAGM 

The diaphragm is a thin musculotendinous structure 
that fills the inferior thoracic aperture and separates the 
thoracic cavity from the abdominal cavity (Fig. 3.33 and 
see Chapter 4). It is attached peripherally to the: 

■ xiphoid process of the sternum, 

■ costal margin of the thoracic wall, 

■ ends of ribs XI and XII, 

■ ligaments that span across structures of the posterior 
abdominal wall, and 

■ vertebrae of the lumbar region. 


From these peripheral attachments, muscle fibers con¬ 
verge to join the central tendon. The pericardium is 
attached to the middle part of the central tendon. 

In the median sagittal plane, the diaphragm slopes 
inferiorly from its anterior attachment to the xiphoid, 
approximately at vertebral level TVIII/IX, to its posterior 
attachment to the median arcuate ligament, crossing 
anteriorly to the aorta at approximately vertebral level 
TXII. 

Structures traveling between the thorax and abdomen 
pass through the diaphragm or between the diaphragm 
and its peripheral attachments: 

■ The inferior vena cava passes through the central 
tendon at approximately vertebral level TVIII. 



Right phrenic nerve 
Right pericardiacophrenic artery 


Right vagus nerve 


Esophagus 


Inferior vena cava 


Central tendon of 
diaphragm 


Phrenic nerves 


Inferior phrenic arteries - 


Left phrenic nerve 

Left pericardiacophrenic artery 

Left vagus nerve 

— Internal thoracic arteries 

Esophageal hiatus 


Aortic hiatus 


Superior epigastric artery 


Musculophrenic artery 

Right crus 

Abdominal aorta 


Fig. 3.33 Diaphragm. 


161 






























Thorax 


■ The esophagus passes through the muscular part of the 
diaphragm, just to the left of midline, approximately at 
vertebral level TX. 

■ The vagus nerves pass through the diaphragm with the 
esophagus. 

■ The aortapasses behind the posterior attachment of the 
diaphragm at vertebral level TXII. 

■ The thoracic duct passes behind the diaphragm with the 
aorta. 

■ The azygos and hemiazygos veins may also pass through 
the aortic hiatus or through the crura of the 
diaphragm. 

Other structures outside the posterior attachments of 
the diaphragm lateral to the aortic hiatus include the 
sympathetic trunks. The greater, lesser, and least splanch¬ 
nic nerves penetrate the crura. 

Arterial supply 

The arterial supply to the diaphragm is from vessels that 
arise superiorly and inferiorly to it (see Fig. 3.33). From 
above, pericardiacophrenic and musculophrenic arteries 
supply the diaphragm. These vessels are branches of the 
internal thoracic arteries. Superior phrenic arteries, 
which arise directly from lower parts of the thoracic 
aorta, and small branches from intercostal arteries con¬ 
tribute to the supply. The largest arteries supplying the dia¬ 
phragm arise from below it. These arteries are the inferior 
phrenic arteries, which branch directly from the abdomi¬ 
nal aorta. 

Venous drainage 

Venous drainage of the diaphragm is by veins that gener¬ 
ally parallel the arteries. The veins drain into: 

■ the brachiocephalic veins in the neck, 

■ the azygos system of veins, or 

■ abdominal veins (left suprarenal vein and inferior vena 
cava). 

Innervation 

The diaphragm is innervated by the phrenic nerves (C3, 
C4, and C5), which penetrate the diaphragm and innervate 
it from its abdominal surface. 

Contraction of the domes of the diaphragm flattens 
the diaphragm, thereby increasing thoracic volume. Move¬ 
ments of the diaphragm are essential for normal 
breathing. 


MOVEMENTS OF THE THORACIC WALL 
AND DIAPHRAGM DURING BREATHING 

One of the principal functions of the thoracic wall and the 
diaphragm is to alter the volume of the thorax and thereby 
move air in and out of the lungs. 

During breathing, the dimensions of the thorax change 
in the vertical, lateral, and anteroposterior directions. 
Elevation and depression of the diaphragm significantly 
alter the vertical dimensions of the thorax. Depression 
results when the muscle fibers of the diaphragm contract. 
Elevation occurs when the diaphragm relaxes. 

Changes in the anteroposterior and lateral dimensions 
result from elevation and depression of the ribs (Fig. 3.34). 
The posterior ends of the ribs articulate with the vertebral 
column, whereas the anterior ends of most ribs articulate 
with the sternum or adjacent ribs. 

Because the anterior ends of the ribs are inferior to the 
posterior ends, when the ribs are elevated, they move the 
sternum upward and forward. Also, the angle between 
the body of the sternum and the manubrium may become 
slightly less acute. When the ribs are depressed, the sternum 
moves downward and backward. This “pump handle” 
movement changes the dimensions of the thorax in the 
anteroposterior direction (Fig. 3.34A). 

As well as the anterior ends of the ribs being lower than 
the posterior ends, the middles of the shafts tend to be 
lower than the two ends. When the shafts are elevated, the 
middles of the shafts move laterally. This “bucket handle” 
movement increases the lateral dimensions of the thorax 
(Fig. 3.34B). 

Any muscles attaching to the ribs can potentially move 
one rib relative to another and therefore act as accessory 
respiratory muscles. Muscles in the neck and the abdomen 
can fix or alter the positions of upper and lower ribs. 

PLEURALCAVITIES 

Two pleural cavities, one on either side of the mediasti¬ 
num, surround the lungs (Fig. 3.35): 

■ Superiorly, they extend above rib I into the root of 
the neck. 

■ Inferiorly, they extend to a level just above the costal 
margin. 

■ The medial wall of each pleural cavity is the 
mediastinum. 


162 




Regional anatomy • Pleural Cavities 


3 



Superior and anterior 
movement of sternum 


A 



Bucket 

handle 

movement 


Elevation of lateral 


shaft of rib 


Fig. 3.34 Movement of thoracic wall during breathing. A. Pump 
handle movement of ribs and sternum. B. Bucket handle 
movement of ribs. 



Rib VIII 


Rib X 


Diaphragm 


Parietal pleura 
Visceral pleura 
Pleural cavity 

Mediastinum 


Rib I 


Right 

lung 


Left lung 


Fig. 3.35 Pleural cavities. 


Pleura 

Each pleural cavity is lined by a single layer of flat cells, 
mesothelium, and an associated layer of supporting con¬ 
nective tissue; together, they form the pleura. 

The pleura is divided into two major types, based on 
location: 

■ Pleura associated with the walls of a pleural cavity is 

parietal pleura (Fig. 3.35). 

■ Pleura that reflects from the medial wall and onto the 
surface of the lung is visceral pleura (Fig. 3.35), which 
adheres to and covers the lung. 


163 
























Thorax 


Each pleural cavity is the potential space enclosed 
between the visceral and parietal pleurae. They normally 
contain only a very thin layer of serous fluid. As a result, 
the surface of the lung, which is covered by visceral pleura, 
directly opposes and freely slides over the parietal pleura 
attached to the wall. 

Parietal pleura 

The names given to the parietal pleura correspond to 
the parts of the wall with which they are associated 
(Fig. 3.36): 

■ Pleura related t o the ribs and intercostal spaces i s termed 

the costal part. 


■ Pleura covering the diaphragm is the diaphragmatic 
part. 

■ Pleura covering the mediastinum is the mediastinal 
part. 

■ The dome-shaped layer of parietal pleura lining the cer¬ 
vical extension of the pleural cavity is cervical pleura 
(dome of pleura or pleural cupola). 

Covering the superior surface of the cervical pleura is a 
distinct dome-like layer of fascia, the suprapleural mem¬ 
brane (Fig. 3.36). This connective tissue membrane is 
attached laterally to the medial margin of the first rib and 
behind to the transverse process of vertebra CVII. Superi¬ 
orly, the membrane receives muscle fibers from some of the 



Pleura surrounding 
structures in root 
of lung 


Pulmonary ligament 


Costal part 


Mediastinal part 


Diaphragmatic part 


Suprapleural membrane 


Cervical pleura 


164 


Fig. 336 Parietal pleura. 











Regional anatomy • Pleural Cavities 


3 


deep muscles in the neck (scalene muscles) that function 
to keep the membrane taught. The suprapleural mem¬ 
brane provides apical support for the pleural cavity in the 
root of the neck. 

In the region of vertebrae TV to TVII, the mediastinal 
pleura reflects off the mediastinum as a tubular, sleeve-like 
covering for structures (i.e., airway, vessels, nerves, lym¬ 
phatics) that pass between the lung and mediastinum. This 
sleeve-like covering, and the structures it contains, forms 
the root of the lung. The root joins the medial surface 
of the lung at an area referred to as the hilum of the 
lung. Here, the mediastinal pleura is continuous with the 
visceral pleura. 

The parietal pleural is innervated by somatic afferent 
fibers. The costal pleura is innervated by branches from the 
intercostal nerves, and pain would be felt in relation to the 
thoracic wall. The diaphragmatic pleura and the mediasti¬ 
nal pleura are innervated mainly by the phrenic nerves 
(originating at spinal cord levels C3, C4, and C5). Pain from 
these areas would refer to the C3, C4, and C5 dermatomes 
(lateral neck and the supraclavicular region of the 
shoulder). 


Peripheral reflections 

The peripheral reflections of parietal pleura mark the 
extent of the pleural cavities (Fig. 3.37). 

Superiorly, the pleural cavity can project as much as 
3-4 cm above the first costal cartilage but does not extend 
above the neck of rib I. This limitation is caused by the 
inferior slope of rib I to its articulation with the 
manubrium. 

Anteriorly, the pleural cavities approach each other pos¬ 
terior to the upper part of the sternum. However, posterior 
to the lower part of the sternum, the parietal pleura does 
not come as close to the midline on the left side as it does 
on the right because the middle mediastinum, containing 
the pericardium and heart, bulges to the left. 

Interiorly, the costal pleura reflects onto the diaphragm 
above the costal margin. In the midclavicular line, the 
pleural cavity extends interiorly to approximately rib VIII. 
In the midaxillary line, it extends to rib X. From this point, 
the inferior margin courses somewhat horizontally, cross¬ 
ing ribs XI and XII to reach vertebra TXII. From the mid- 
clavicular line to the vertebral column, the inferior 



Vertebra TXII (posterior) 

Rib X (lateral) 


Rib VIII (anterior) 


Midclavicular line 


Midaxillary line 


Fig. 337 Pleural reflections. 


165 















Thorax 


boundary of the pleura can be approximated by a line that 
runs between rib VIII, rib X, and vertebra TXII. 

Visceral pleura 

The visceral pleura is continuous with the parietal pleura 
at the hilum of each lung, where structures enter and leave 
the organ. The visceral pleura is firmly attached to the 
surface of the lung, including both opposed surfaces of the 
fissures that divide the lungs into lobes. 

Although the visceral pleura is innervated by visceral 
afferent nerves that accompany bronchial vessels, pain is 
generally not elicited from this tissue. 

Pleural recesses 

The lungs do not completely fill the anterior or posterior 
inferior regions of the pleural cavities (Fig. 3.38). This 
results in recesses in which two layers of parietal pleura 
become opposed. Expansion of the lungs into these spaces 
usually occurs only during forced inspiration; the recesses 


also provide potential spaces in which fluids can collect and 
from which fluids can be aspirated. 

Costomediastinal recesses 

Anteriorly, a costomediastinal recess occurs on each 
side where costal pleura is opposed to mediastinal pleura. 
The largest is on the left side in the region overlying the 
heart (Fig. 3.38). 

Costodiaphragmatic recesses 

The largest and clinically most important recesses are 
the costodiaphragmatic recesses, which occur in each 
pleural cavity between the costal pleura and diaphragmatic 
pleura (Fig. 3.38). The costodiaphragmatic recesses are the 
regions between the inferior margin of the lungs and infe¬ 
rior margin of the pleural cavities. They are deepest after 
forced expiration and shallowest after forced inspiration. 

During quiet respiration, the inferior margin of the lung 
crosses rib VI in the midclavicular line and rib VIII in the 


Midclavicular line- 1 



Midaxillary line 


Rib VI (anterior) 


Vertebra TX (posterior) 
Rib VIII (lateral) 


Costodiaphragmatic recess 


Costomediastinal recess 


166 


I 

Fig. 3.18 Parietal pleural reflections and recesses. 
















Regional anatomy • Pleural Cavities 


3 


midaxillary line, and then courses somewhat horizontally 
to reach the vertebral column at vertebral level TX. Thus, 
from the midclavicular line and around the thoracic wall 
to the vertebral column, the inferior margin of the lung 
can be approximated by a line running between rib VI, rib 
VIII, and vertebra TX. The inferior margin of the pleural 
cavity at the same points is rib VIII, rib X, and vertebra 
TXII. The costodiaphragmatic recess is the region between 
the two margins. 

During expiration, the inferior margin of the lung rises 
and the costodiaphragmatic recess becomes larger. 

In the clinic 
Pleural effusion 

A pleural effusion occurs when excess fluid accumulates 
within the pleural space. As the fluid accumulates 
within the pleural space the underlying lung is 
compromised and may collapse as the volume of fluid 
increases. Once a pleural effusion has been diagnosed, 
fluid often will be aspirated to determine the cause, 
which can include infection, malignancy, cardiac failure, 
hepatic disease, and pulmonary embolism. 


In the clinic 
Pneumothorax 

A pneumothorax is a collection of gas or air within the 
pleural cavity. When air enters the pleural cavity the 
tissue elasticity of the parenchyma causes the lung to 
collapse within the chest, impairing the lung function. 
Occasionally, the gas within the pleural cavity may 
accumulate to such an extent that the mediastinum is 
"pushed" to the opposite side, compromising the other 
lung. This is termed a tension pneumothorax and 
requires urgent treatment. 

Most pneumothoraces are spontaneous (i.e., they 
occur in the absence of no known pathology and no 
known lung disease). In addition, pneumothoraces may 
occur as a result of trauma, inflammation, smoking, and 
other underlying pulmonary diseases. 

The symptoms of pneumothorax are often 
determined by the degree of air leak and the rate at 
which the accumulation of gas occurs and the ensuing 
lung collapses. They include pain, shortness of breath, 
and cardiorespiratory collapse, if severe. 

Lungs 

The two lungs are organs of respiration and lie on either 
side of the mediastinum surrounded by the right and left 
pleural cavities. Air enters and leaves the lungs via main 
bronchi, which are branches of the trachea. 


The pulmonary arteries deliver deoxygenated blood 
to the lungs from the right ventricle of the heart. Oxygen¬ 
ated blood returns to the left atrium via the pulmonary 
veins. 

The right lung is normally a little larger than the left 
lung because the middle mediastinum, containing the 
heart, bulges more to the left than to the right. 

Each lung has a half-cone shape, with a base, apex, two 
surfaces, and three borders (Fig. 3.39). 

■ The base sits on the diaphragm. 

■ The apex projects above rib I and into the root of 
the neck. 

■ The two surfaces—the costal surface lies immediately 
adjacent to the ribs and intercostal spaces of the 
thoracic wall. The mediastinal surface lies against 
the mediastinum anteriorly and the vertebral column 
posteriorly and contains the comma-shaped hilum 
of the lung, through which structures enter and 
leave. 

■ The three borders—the inferior border of the lung is 
sharp and separates the base from the costal surface. 
The anterior and posterior borders separate the 
costal surface from the medial surface. Unlike the ante¬ 
rior and inferior borders, which are sharp, the posterior 
border is smooth and rounded. 

The lungs lie directly adjacent to, and are indented by, 
structures contained in the overlying area. The heart and 
major vessels form bulges in the mediastinum that indent 
the medial surfaces of the lung; the ribs indent the costal 
surfaces. Pathology, such as tumors, or abnormalities in 
one structure can affect the related structure. 

Root and hilum 

The root of each lung is a short tubular collection of struc¬ 
tures that together attach the lung to structures in the 
mediastinum (Fig. 3.40). It is covered by a sleeve of medi¬ 
astinal pleura that reflects onto the surface of the lung as 
visceral pleura. The region outlined by this pleural reflec¬ 
tion on the medial surface of the lung is the hilum, where 
structures enter and leave. 

A thin blade-like fold of pleura projects inferiorly from 
the root of the lung and extends from the hilum to the 
mediastinum. This structure is the pulmonary ligament. 
It may stabilize the position of the inferior lobe and may 
also accommodate the down-and-up translocation of 
structures in the root during breathing. 

In the mediastinum, the vagus nerves pass immediately 
posterior to the roots of the lungs, while the phrenic nerves 
pass immediately anterior to them. 


167 



Thorax 


Right lung 


Left lung 




Hilum 


Posterior 

border 


Inferior border 
Base (diaphragmatic surface) 


Anterior border 


Apex 


Bronchus 


Pulmonary 

artery 

Pulmonary 

veins 


Costal surface 


Mediastinal 

surface 


Fig. 3.39 Lungs. 


Pulmonary 

artery 

Pulmonary 

veins 




Hilum 


Pulmonary artery 
(deoxygenated blood) 

Pulmonary veins 
(oxygenated blood) 


Root 


Bronchus 


Right lung 


Pulmonary ligament 


Left lung 


168 


Fig. 3.40 Roots and hi la of the lungs. 

















Regional anatomy • Pleural Cavities 


3 


Within each root and located in the hilum are: 

■ a pulmonary artery, 

■ two pulmonary veins, 

■ a main bronchus, 

■ bronchial vessels, 

■ nerves, and 

■ lymphatics. 

Generally, the pulmonary artery is superior at the hilum, 
the pulmonary veins are inferior, and the bronchi are 
somewhat posterior in position. 

On the right side, the lobar bronchus to the superior lobe 
branches from the main bronchus in the root, unlike on 
the left where it branches within the lung itself, and is 
superior to the pulmonary artery. 

Right lung 

The right lung has three lobes and two fissures (Fig. 
3.41 A). Normally, the lobes are freely movable against 
each other because they are separated, almost to the hilum, 
by invaginations of visceral pleura. These invaginations 
form the fissures: 

■ The oblique fissure separates the inferior lobe 
(lower lobe) from the superior lobe and the middle 
lobe of the right lung. 

■ The horizontal fissure separates the superior lobe 
(upper lobe) from the middle lobe. 

The approximate position of the oblique fissure on a 
patient, in quiet respiration, can be marked by a curved line 
on the thoracic wall that begins roughly at the spinous 
process of the vertebra TIV level of the spine, crosses the 
fifth interspace laterally, and then follows the contour of 
rib VI anteriorly (see p. 239). 

The horizontal fissure follows the fourth intercostal 
space from the sternum until it meets the oblique fissure as 
it crosses rib V. 

The orientations of the oblique and horizontal fissures 
determine where clinicians should listen for lung sounds 
from each lobe. 

The largest surface of the superior lobe is in contact 
with the upper part of the anterolateral wall and the apex 
of this lobe projects into the root of the neck. The surface 
of the middle lobe lies mainly adjacent to the lower anterior 
and lateral wall. The costal surface of the inferior lobe is in 
contact with the posterior and inferior walls. 

When listening to lung sounds from each of the lobes, 
it is important to position the stethoscope on those areas 
of the thoracic wall related to the underlying positions of 
the lobes (see p. 240). 


The medial surface of the right lung lies adjacent to a 
number of important structures in the mediastinum and 
the root of the neck (Fig. 3.4IB). These include the: 

■ heart, 

■ inferior vena cava, 

■ superior vena cava, 

■ azygos vein, and 

■ esophagus. 

The right subclavian artery and vein arch over and are 
related to the superior lobe of the right lung as they pass 
over the dome of the cervical pleura and into the axilla. 

Left lung 

The left lung is smaller than the right lung and has two 
lobes separated by an oblique fissure (Fig. 3.42A). The 
oblique fissure of the left lung is slightly more oblique 
than the corresponding fissure of the right lung. 

During quiet respiration, the approximate position of 
the left oblique fissure can be marked by a curved line 
on the thoracic wall that begins between the spinous 
processes of vertebrae Till and TIV, crosses the fifth inter¬ 
space laterally, and follows the contour of rib VI anteriorly 
(see pp. 237-238). 

As with the right lung, the orientation of the oblique 
fissure determines where to listen for lung sounds from 
each lobe. 

The largest surface of the superior lobe is in contact 
with the upper part of the anterolateral wall, and the apex 
of this lobe projects into the root of the neck. The costal 
surface of the inferior lobe is in contact with the posterior 
and inferior walls. 

When listening to lung sounds from each of the lobes, 
the stethoscope should be placed on those areas of the 
thoracic wall related to the underlying positions of the 
lobes (see p. 240). 

The inferior portion of the medial surface of the left 
lung, unlike the right lung, is notched because of the 
heart’s projection into the left pleural cavity from the 
middle mediastinum. 

From the anterior border of the lower part of the supe¬ 
rior lobe a tongue-like extension (the lingula of the left 
lung) projects over the heart bulge. 

The medial surface of the left lung lies adjacent to a 
number of important structures in the mediastinum and 
root of the neck (Fig. 3.42B). These include the: 

■ heart, 

■ aortic arch, 

■ thoracic aorta, and 

■ esophagus. 169 



Thorax 


A 



Superior lobe 


Horizontal fissure 


Middle lobe 


Oblique fissure 


Inferior lobe 



Right brachiocephalic vein 
Left brachiocephalic vein 

Superior vena cava 


Pulmonary artery 

Pulmonary veins - 

Heart — 


Inferior vena cava 


Diaphragm 


Rib I 


Anterior 


Subclavian artery 


Subclavian 


Posterior 


Bronchus to 
superior lobe 

Bronchus 

Esophagus 

Azygos vein 


170 


Fig. 3.41 A. Right lung. B. Major structures related to the right lung. 





























Regional anatomy • Pleural Cavities 


3 


A 


Oblique fissure 


Inferior lobe 



Superior lobe 


Lingula 



Posterior 

Rib I 


Anterior 

Left subclavian artery 


Left brachiocephalic vein 


Bronchus 

Esophagus 


Thoracic aorta 


Aortic arch 


Pulmonary artery 


Pulmonary veins 

Heart 


B 

Fig. 3.42 A. Left lung. B. Major structures related to the left lung. 


Diaphragm 


171 






















Thorax 


The left subclavian artery and vein arch over and are 
related to the superior lobe of the left lung as they pass over 
the dome of the cervical pleura and into the axilla. 

Bronchial tree 

The trachea is a flexible tube that extends from vertebral 
level CVI in the lower neck to vertebral level TIV/V in the 
mediastinum where it bifurcates into a right and a left 
main bronchus (Fig. 3.43). The trachea is held open by 


C-shaped transverse cartilage rings embedded in its wall— 
the open part of the C facing posteriorly. The lowest tra¬ 
cheal ring has a hook-shaped structure, the carina, that 
projects backwards in the midline between the origins of 
the two main bronchi. The posterior wall of the trachea is 
composed mainly of smooth muscle. 

Each main bronchus enters the root of a lung and 
passes through the hilum into the lung itself. The right 
main bronchus is wider and takes a more vertical course 


A 


B 



Segmental bronchi 
of middle lobe 


Lateral bronchopulmonary segment 
of middle lobe of right lung 



Branch of pulmonary artery 


Medial bronchopulmonary segment 
of middle lobe of right lung 


172 


Fig. 3.43 A. Bronchial tree. B. Bronchopulmonary segments. 












Regional anatomy • Pleural Cavities 


3 


through the root and hilum than the left main bronchus 
(Fig. 3.43A). Therefore, inhaled foreign bodies tend to 
lodge more frequently on the right side than on the left. 

The main bronchus divides within the lung into lobar 
bronchi (secondary bronchi), each of which supplies a 
lobe. On the right side, the lobar bronchus to the superior 
lobe originates within the root of the lung. 

The lobar bronchi further divide into segmental 
bronchi (tertiary bronchi), which supply bronchopulmo¬ 
nary segments (Fig. 3.43B). 

Within each bronchopulmonary segment, the segmen¬ 
tal bronchi give rise to multiple generations of divisions 
and, ultimately, to bronchioles, which further subdivide 
and supply the respiratory surfaces. The walls of the 
bronchi are held open by discontinuous elongated plates of 
cartilage, but these are not present in bronchioles. 


Bronchopulmonary segments 

A bronchopulmonary segment is the area of lung 
supplied by a segmental bronchus and its accompanying 
pulmonary artery branch. 

Tributaries of the pulmonary vein tend to pass interseg- 
mentally between and around the margins of segments. 

Each bronchopulmonary segment is shaped like an 
irregular cone, with the apex at the origin of the segmental 
bronchus and the base projected peripherally onto the 
surface of the lung. 

A bronchopulmonary segment is the smallest function¬ 
ally independent region of a lung and the smallest area of 
lung that can be isolated and removed without affecting 
adjacent regions. 

There are ten bronchopulmonary segments in each 
lung (Fig. 3.44); some of them fuse in the left lung. 


Medial view 


Lateral view 


Apical segment (S I) 

Superior lobe 


Anterior segment 
(S III) 


Medial 
segment (S V) 

Middle lobe 



Anterior basal 
segment (S VIII) 


Posterior segment (S II) 


Superior segment 
(S VI) 

Inferior lobe 

Medial basal 
segment (S VII) 


Posterior basal 
segment (S X) 


Lateral basal segment (S IX)' 


Apical segment (S I) 



Anterior segment 
(SI 


Medial 

segment 

(SV) 


Lateral 
segment 
(S IV) 


Anterior basal 
segment (S VIII) 


Apicoposterior segment (S I & II) 


Superior 
segment (S VI) 

Inferior lobe 

Posterior basal 
segment (S X) 


Medial basal 
segment (S VII) 


Superior lobe 



Anterior segment 
(SIN) 


Superior lingular 
segment (S IV) 

Inferior lingular 
segment (S V) 

Anterior basal 
segment (S VIII) 


Lateral basal segment (S IX) 



Superior 
segment 
(S VI) 


Posterior 
basal 
segment 
(S X) 


Fig. 3.44 Bronchopulmonary segments. A. Right lung. B. Left lung. (Bronchopulmonary segments are numbered and named.) 


173 

















Thorax 


Pulmonary arteries 

The right and left pulmonary arteries originate from the 
pulmonary trunk and carry deoxygenated blood to the 
lungs from the right ventricle of the heart (Fig. 3.45). 

The bifurcation of the pulmonary trunk occurs to 
the left of the midline just inferior to vertebral level TIV/V, 
and anteroinferiorly to the left of the bifurcation of the 
trachea. 

Right pulmonary artery 

The right pulmonary artery is longer than the left and 
passes horizontally across the mediastinum (Fig. 3.45). 
It passes: 

■ anteriorly and slightly interiorly to the tracheal bifur¬ 
cation and anteriorly to the right main bronchus, 
and 

■ posteriorly to the ascending aorta, superior vena cava, 
and upper right pulmonary vein. 

The right pulmonary artery enters the root of the lung 
and gives off a large branch to the superior lobe of the 
lung. The main vessel continues through the hilum of 
the lung, gives off a second (recurrent) branch to the 
superior lobe, and then divides to supply the middle and 
inferior lobes. 

Left pulmonary artery 

The left pulmonary artery is shorter than the right and 
lies anterior to the descending aorta and posterior to the 
superior pulmonary vein (Fig. 3.45). It passes through the 
root and hilum and branches within the lung. 


Pulmonary veins 

On each side a superior pulmonary vein and an infe¬ 
rior pulmonary vein carry oxygenated blood from the 
lungs back to the heart (Fig. 3.45). The veins begin at the 
hilum of the lung, pass through the root of the lung, and 
immediately drain into the left atrium. 

Bronchial arteries and veins 

The bronchial arteries (Fig. 3.45) and veins constitute the 
“nutritive” vascular system of the pulmonary tissues 
(bronchial walls and glands, walls of large vessels, and vis¬ 
ceral pleura). They interconnect within the lung with 
branches of the pulmonary arteries and veins. 

The bronchial arteries originate from the thoracic aorta 
or one of its branches: 

■ A single right bronchial artery normally arises from 
the third posterior intercostal artery (but occasionally, 
it originates from the upper left bronchial artery). 

■ Two left bronchial arteries arise directly from the 
anterior surface of the thoracic aorta—the superior 
left bronchial artery arises at vertebral level TV, and 
the inferior one inferior to the left bronchus. 

The bronchial arteries run on the posterior surfaces of 
the bronchi and ramify in the lungs to supply pulmonary 
tissues. 

The bronchial veins drain into: 

■ either the pulmonary veins or the left atrium, and 

■ into the azygos vein on the right or into the superior 
intercostal vein or hemiazygos vein on the left. 


174 


Regional anatomy • Pleural Cavities 


3 


A 



Right pulmonary artery 


Bronchial vessels 
on posterior surface 
of bronchi 


Left pulmonary artery 

Inferior left bronchial artery 


Pulmonary trunk 


Esophagus 


Right bronchial artery 

(branch from right third 
posterior intercostal artery) 


Right pulmonary 
veins 


Left pulmonary veins 


Pulmonary ligament 
Thoracic aorta 


Aortic arch 


Superior left bronchial artery 



Superior vena cava Ascending aorta Pulmonary trunk 


Right main bronchus Esophagus 


Left pulmonary artery 


Thoracic aorta 


Superior vena cava Ascending aorta Pulmonary trunk 



Right pulmonary artery Esophagus Thoracic aorta 


Fig. 3.45 Pulmonary vessels. A. Diagram of an anterior view. B. Axial computed tomography image showing the left pulmonary artery 
branching from the pulmonary trunk. C. Axial computed tomography image (just inferior to the image in B) showing the right pulmonary 
artery branching from the pulmonary trunk. 


175 










































Thorax 


Innervation 

Structures of the lung, and the visceral pleura, are supplied 
by visceral afferents and efferents distributed through 
the anterior pulmonary plexus and posterior pulmonary 
plexus (Fig. 3.46). These interconnected plexuses lie ante¬ 
riorly and posteriorly to the tracheal bifurcation and main 
bronchi. The anterior plexus is much smaller than the pos¬ 
terior plexus. 

Branches of these plexuses, which ultimately originate 
from the sympathetic trunks and vagus nerves, are distrib¬ 
uted along branches of the airway and vessels. 


Visceral efferents from: 

■ the vagus nerves constrict the bronchioles; 

■ the sympathetic system dilates the bronchioles. 

Lymphatic drainage 

Superficial, or subpleural, and deep lymphatics of the lung 
drain into lymph nodes called tracheobronchial nodes 
around the roots of lobar and main bronchi and along the 
sides of the trachea (Fig. 3.47). As a group, these lymph 
nodes extend from within the lung, through the hilum and 
root, and into the posterior mediastinum. 



Cervical cardiac nerves 


Right vagus nerve 


Anterior pulmonary plexus 


Left recurrent laryngeal nerve 


Left vagus nerve 


Ligamentum arteriosum 


Posterior pulmonary plexus 

Esophageal plexus 


Sympathetic trunk 


176 


Fig. 3.46 Pulmonary innervation. 
































Regional anatomy • Pleural Cavities 


3 


Thoracic duct 



Thoracic duct 


Left bronchomediastinal trunk 


Left parasternal 
lymphatic vessel 


Diaphragm 


Cisterna chyli 


Brachiocephalic node 


Right bronchomediastinal trunk 


Parasternal nodes 


Tracheobronchial nodes 


Right parasternal 
lymphatic vessel 


Fig. 3.47 Lymphatic drainage of lungs. 


177 

























Thorax 


Efferent vessels from these nodes pass superiorly along 
the trachea to unite with similar vessels from parasternal 
nodes and brachiocephalic nodes, which are anterior to 
brachiocephalic veins in the superior mediastinum, to 


form the right and left bronchomediastinal trunks. 

These trunks drain directly into deep veins at the base of the 
neck, or may drain into the right lymphatic trunk or tho¬ 
racic duct. 


In the clinic 
Imaging the lungs 

Medical imaging of the lungs is important because they 
are one of the commonest sites for disease in the body. 
While the body is at rest, the lungs exchange up to 5 L 
of air per minute, and this may contain pathogens and 
other potentially harmful elements (e.g., allergens). 
Techniques to visualize the lung range from plain chest 
radiographs to high-resolution computed tomography 
(CT), which enables precise localization of a lesion 
within the lung. 


In the clinic 
High-resolution lung CT 

High-resolution computed tomography (HRCT) is a 
diagnostic method for assessing the lungs but more 
specifically the interstitium of the lungs. The technique 
involves obtaining narrow cross-sectional slices of 1 to 
2 mm. These scans enable the physician and radiologist 
to view the patterns of disease and their distribution. 
Diseases that may be easily demonstrated using this 
procedure include emphysema, pneumoconiosis (coal 
worker's pneumoconiosis), and asbestosis. 


In the clinic 
Bronchoscopy 

Patients who have an endobronchial lesion (i.e., 
a lesion within a bronchus) may undergo bronchoscopic 
evaluation of the trachea and its main branches (Fig. 3.48). 



Left main bronchus 


The bronchoscope is passed through the nose into the 
oropharynx and is then directed by a control system past 
the vocal cords into the trachea. The bronchi are 
inspected and, if necessary, small biopsies are obtained. 



Right main bronchus 


Tumor- 


178 


Fig. 3.48 Bronchoscopic evaluation. A. Of the lower end of the trachea and its main branches. B. Of tracheal bifurcation showing a 
tumor at the carina. 









Regional anatomy • Pleural Cavities 


3 


In the clinic 
Lung cancer 

It is important to stage lung cancer because the treatment 
depends on its stage. 

If a small malignant nodule is found within the lung, it 
can sometimes be excised and the prognosis is excellent. 
Unfortunately, many patients present with a tumor mass 
that has invaded structures in the mediastinum or the 
pleurae or has metastasized. The tumor may then be 
inoperable and is treated with radiotherapy and 
chemotherapy. 

Spread of the tumor is by lymphatics to lymph nodes 
within the hila, mediastinum, and root of the neck. 


A key factor affecting the prognosis and ability to cure 
the disease is the distant spread of metastases. Imaging 
methods to assess spread include plain radiography 
(Fig. 3.49A), computed tomography (CT; Fig. 3.49B), 
and magnetic resonance imaging (MRI). Increasingly, 
radionuclide studies using fluorodeoxyglucose positron 
emission tomography (FDG PET; Fig. 3.49C) are 
being used. 

In FDG PET a gamma radiation emitter is attached to a 
glucose molecule. In areas of high metabolic activity (i.e., 
the tumor), excessive uptake occurs and is recorded by a 
gamma camera. 


-Tumor 




—Tumor 



Fig. 3.49 Imaging of the lungs. A. Standard posteroanterior view of the chest showing tumor in upper right lung. B. Axial CT image of 
lungs showing tumor in right lung. C. Radionuclide study using FDG PET showing a tumor in the right lung. 


179 







Thorax 


MEDIASTINUM 

The mediastinum is a broad central partition that sepa¬ 
rates the two laterally placed pleural cavities (Fig. 3.50). It 
extends: 

■ from the sternum to the bodies of the vertebrae, and 

■ from the superior thoracic aperture to the diaphragm 
(Fig. 3.51). 


The area anterior to the pericardial sac and posterior to 
the body of the sternum is the anterior mediastinum. The 
region posterior to the pericardial sac and the diaphragm 
and anterior to the bodies of the vertebrae is the posterior 
mediastinum. The area in the middle, which includes the 
pericardial sac and its contents, is the middle mediastinum 
(Fig. 3.52). 

Middle mediastinum 


The mediastinum contains the thymus gland, the peri¬ 
cardial sac, the heart, the trachea, and the major arteries 
and veins. 

Additionally, the mediastinum serves as a passageway 
for structures such as the esophagus, thoracic duct, and 
various components of the nervous system as they traverse 
the thorax on their way to the abdomen. 

For organizational purposes, the mediastinum is subdi¬ 
vided into several smaller regions. A transverse plane 
extending from the sternal angle (the junction between the 
manubrium and the body of the sternum) to the interver¬ 
tebral disc between vertebrae TIV and TV separates the 
mediastinum into the: 

■ superior mediastinum, and 

■ inferior mediastinum, which is further partitioned 
into the anterior, middle, and posterior mediasti¬ 
num by the pericardial sac. 


Mediastinum Left pleural cavity 



Right pleural cavity 


180 


Fig. 3.50 Cross-section of the thorax showing the position of the 
mediastinum. 


The middle mediastinum is centrally located in the tho¬ 
racic cavity. It contains the pericardium, heart, origins of 
the great vessels, various nerves, and smaller vessels. 


Superior thoracic aperture 



Sternal angle 


Sternum 


Diaphragm 


Fig. 3.51 Lateral view of the mediastinum. 






















Regional anatomy • Mediastinum 


3 



Middle mediastinum 


Posterior mediastinum 


Sternal angle 


Superior — 
mediastinum 


Anterior 

mediastinum 


Inferior — 
mediastinum 



Junction between fibrous 
pericardium and adventitia 
of great vessels 


Visceral layer 
of serous 
pericardium 
(epicardium) 


Pericardial 

cavity 


Parietal layer 
of serous 
pericardium 


Fibrous 

pericardium 


Fig. 3.53 Sagittal section of the pericardium. 


■ The visceral layer (epicardium) of serous pericar¬ 
dium adheres to the heart and forms its outer 
covering. 


Fig. 3.52 Subdivisions of the mediastinum. 


Pericardium 

The pericardium is a fibroserous sac surrounding the 
heart and the roots of the great vessels. It consists of two 
components, the fibrous pericardium and the serous peri¬ 
cardium (Fig. 3.53). 

The fibrous pericardium is a tough connective tissue 
outer layer that defines the boundaries of the middle medi¬ 
astinum. The serous pericardium is thin and consists of 
two parts: 

■ The parietal layer of serous pericardium lines the 
inner surface of the fibrous pericardium. 


The parietal and visceral layers of serous pericardium 
are continuous at the roots of the great vessels. The narrow 
space created between the two layers of serous pericar¬ 
dium, containing a small amount of fluid, is the pericar¬ 
dial cavity. This potential space allows for the relatively 
uninhibited movement of the heart. 

Fibrous pericardium 

The fibrous pericardium is a cone-shaped bag with its 
base on the diaphragm and its apex continuous with the 
adventitia of the great vessels (Fig. 3.53). The base is 
attached to the central tendon of the diaphragm and 
to a small muscular area of the diaphragm on the left side. 
Anteriorly, it is attached to the posterior surface of the 
sternum by sternopericardial ligaments. These attach¬ 
ments help to retain the heart in its position in the thoracic 
cavity. The sac also limits cardiac distention. 


181 























Thorax 


The phrenic nerves, which innervate the diaphragm 
and originate from spinal cord levels C3 to C5, pass through 
the fibrous pericardium and innervate the fibrous pericar¬ 
dium as they travel from their point of origin to their final 
destination (Fig. 3.54). Their location, within the fibrous 
pericardium, is directly related to the embryological origin 
of the diaphragm and the changes that occur during 
the formation of the pericardial cavity. Similarly, the 


pericardiacophrenic vessels are also located within and 
supply the fibrous pericardium as they pass through the 
thoracic cavity. 

Serous pericardium 

The parietal layer of serous pericardium is continuous with 
the visceral layer of serous pericardium around the roots 


Trachea 



Left common carotid artery 


Superior vena cava 


Right phrenic nervr 


Left phrenic nerve 


Left pericardiacophrenic 
vessels 


Fig. 3.54 Phrenic nerves and pericardiacophrenic vessels. 


182 































Regional anatomy • Mediastinum 


3 


of the great vessels. These reflections of serous pericardium 
(Fig. 3.55) occur in two locations: 

■ one superiorly, surrounding the arteries, the aorta, and 
the pulmonary trunk; 

■ the second more posteriorly, surrounding the veins, the 
superior and inferior vena cava, and the pulmonary 
veins. 

The zone of reflection surrounding the veins is J-shaped, 
and the cul-de-sac formed within the J, posterior to the left 
atrium, is the oblique pericardial sinus. 

A passage between the two sites of reflected serous peri¬ 
cardium is the transverse pericardial sinus. This sinus 
lies posterior to the ascending aorta and the pulmonary 
trunk, anterior to the superior vena cava, and superior to 
the left atrium. 

When the pericardium is opened anteriorly during 
surgery, a finger placed in the transverse sinus separates 


arteries from veins. A hand placed under the apex of the 
heart and moved superiorly slips into the oblique sinus. 

Vessels and nerves 

The pericardium is supplied by branches from the internal 
thoracic, pericardiacophrenic, musculophrenic, and infe¬ 
rior phrenic arteries, and the thoracic aorta. 

Veins from the pericardium enter the azygos system of 
veins and the internal thoracic and superior phrenic veins. 

Nerves supplying the pericardium arise from the 
vagus nerve [X], the sympathetic trunks, and the phrenic 
nerves. 

It is important to note that the source of somatic sensa¬ 
tion (pain) from the parietal pericardium is carried by 
somatic afferent fibers in the phrenic nerves. For this 
reason, ‘‘pain” related to a pericardial problem may be 
referred to the supraclavicular region of the shoulder or 
lateral neck area dermatomes for spinal cord segments 
C3, C4, and C5. 



Superior vena cava 


Right pulmonary veins — 


Oblique pericardial sinus 

(formed by reflection onto the 
pulmonary veins of heart) 


Ascending aorta 


Arch of aorta 


Cut edge of pericardium 


Thoracic aorta 


Transverse pericardial sinus 

(separates arteries from veins) 


Left pulmonary artery 


Branch of right 
pulmonary artery 


— Left pulmonary veins 


Fig. 3.55 Posterior portion of pericardial sac showing reflections of serous pericardium. 


183 



















Thorax 


In the clinic 
Pericarditis 

Pericarditis is an inflammatory condition of the 
pericardium. Common causes are viral and bacterial 
infections, systemic illnesses (e.g., chronic renal failure), 
and after myocardial infarction. 

Pericarditis must be distinguished from myocardial 
infarction because the treatment and prognosis are 
quite different. As in patients with myocardial infarction, 
patients with pericarditis complain of continuous 
central chest pain that may radiate to one or both arms. 
Unlike myocardial infarction, however, the pain from 
pericarditis may be relieved by sitting forward. An 
electrocardiogram (ECG) is used to help differentiate 
between the two conditions. 


In the clinic 
Pericardial effusion 

Normally, only a tiny amount of fluid is present between 
the visceral and parietal layers of the serous 
pericardium. In certain situations, this space can be 
filled with excess fluid (pericardial effusion). 

Because the fibrous pericardium is a "relatively fixed" 
structure that cannot expand easily, a rapid 
accumulation of excess fluid within the pericardial sac 
compresses the heart (cardiac tamponade), resulting in 
biventricular failure. Removing the fluid with a needle 
inserted into the pericardial sac can relieve the 
symptoms. 


In the clinic 
Constrictive pericarditis 

Abnormal thickening of the pericardial sac (constrictive 
pericarditis) can compress the heart, impairing heart 
function and resulting in heart failure. The diagnosis is 
made by inspecting the jugular venous pulse in the 
neck. In normal individuals, the jugular venous pulse 
drops on inspiration. In patients with constrictive 
pericarditis, the reverse happens and this is called 
Kussmaul's sign. Treatment often involves surgical 
opening of the pericardial sac. 


Heart 

Cardiac orientation 

The general shape and orientation of the heart are that of 
a pyramid that has fallen over and is resting on one of 
its sides. Placed in the thoracic cavity, the apex of this 
pyramid projects forward, downward, and to the left, 
whereas the base is opposite the apex and faces in a 
posterior direction (Fig. 3.56). The sides of the pyramid 
consist of: 

■ a diaphragmatic (inferior) surface on which the 
pyramid rests, 

■ an anterior (sternocostal) surface oriented anteriorly, 

■ a right pulmonary surface, and 

■ a left pulmonary surface. 

Base (posterior surface) and apex 

The base of the heart is quadrilateral and directed pos¬ 
teriorly. It consists of: 

■ the left atrium, 

■ a small portion of the right atrium, and 

■ the proximal parts of the great veins (superior and infe¬ 
rior venae cavae and the pulmonary veins) (Fig. 3.57). 



Diaphragmatic surface 


184 


Fig. 3.56 Schematic illustration of the heart showing orientation, 
surfaces, and margins. 
















Regional anatomy • Mediastinum 


3 



Left pulmonary artery 


Left superior pulmonary vein 


Left atrium 


Left inferior pulmonary vein 


Coronary sinus 


Left ventricle 


Fig. 3.57 Base of the heart. 


Arch of aorta 

Superior vena cava 

Right pulmonary artery 


Right pulmonary veins 

Right atrium 

Sulcus terminalis 


Inferior vena cava 


Right ventricle 


185 



















Thorax 


Because the great veins enter the base of the heart, with 
the pulmonary veins entering the right and left sides of 
the left atrium and the superior and inferior venae cavae 
at the upper and lower ends of the right atrium, the base 
of the heart is fixed posteriorly to the pericardial wall, 
opposite the bodies of vertebrae TV to TVIII (TVI to TIX 
when standing). The esophagus lies immediately posterior 
to the base. 


From the base the heart projects forward, downward, 
and to the left, ending in the apex. The apex of the heart 
is formed by the inferolateral part of the left ventricle 
(Fig. 3.58) and is positioned deep to the left fifth intercostal 
space, 8-9 cm from the midsternal line. 



Superior vena cava 


Ascending aorta 


Right coronary 
artery 

Right atrium 


Right ventricle 


Small cardiac vein 
Inferior vena cava 


Apex 


Left auricle 


Anterior interventricular 
branch of left coronary artery 


Great cardiac vein 


Anterior interventricular groove 


Left ventricle 


Obtuse margin 


Arch of aorta 

Pulmonary trunk 


Inferior margin 


Fig. 3.58 Anterior surface of the heart. 


186 










Regional anatomy • Mediastinum 


3 


Surfaces of the heart 

The anterior surface faces anteriorly and consists 
mostly of the right ventricle, with some of the right 
atrium on the right and some of the left ventricle on the 
left (Fig. 3.58). 

The heart in the anatomical position rests on the dia¬ 
phragmatic surface, which consists of the left ventricle 
and a small portion of the right ventricle separated by the 
posterior interventricular groove (Fig. 3.59). This surface 
faces inferiorly, rests on the diaphragm, is separated from 
the base of the heart by the coronary sinus, and extends 
from the base to the apex of the heart. 

The left pulmonary surface faces the left lung, is 
broad and convex, and consists of the left ventricle and a 
portion of the left atrium (Fig. 3.59). 


The right pulmonary surface faces the right lung, 
is broad and convex, and consists of the right atrium 
(Fig. 3.59). 

Margins and borders 

Some general descriptions of cardiac orientation refer to 
right, left, inferior (acute), and obtuse margins: 

■ The right and left margins are the same as the right 
and left pulmonary surfaces of the heart. 

■ The inferior margin is defined as the sharp edge 
between the anterior and diaphragmatic surfaces of the 
heart (Figs 3.56 and 3.58) —it is formed mostly by the 
right ventricle and a small portion of the left ventricle 
near the apex. 



Arch of aorta 


Right pulmonary artery 


Inferior vena cava 


Left ventricle 


Marginal branch of 
right coronary artery 


Left pulmonary artery 


Superior vena cava 


Left pulmonary veins — 


Left atrium 


Coronary sinus 


— Right pulmonary veins 

Right atrium 


Middle cardiac vein 


Posterior interventricular 
branch of right coronary 
artery 


Right ventricle 


Posterior interventricular groove 


Fig. 3.59 Diaphragmatic surface of the heart. 


187 













Thorax 


188 


■ The obtuse margin separates the anterior and left pul¬ 
monary surfaces (Fig. 3.56) —it is round and extends 
from the left auricle to the cardiac apex (Fig. 3.58), and 
is formed mostly by the left ventricle and superiorly by 
a small portion of the left auricle. 

For radiological evaluations, a thorough understanding 
of the structures defining the cardiac borders is critical. 
The right border in a standard posteroanterior view con¬ 
sists of the superior vena cava, the right atrium, and the 
inferior vena cava (Fig. 3.60A). The left border in a similar 
view consists of the arch of the aorta, the pulmonary 
trunk, and the left ventricle. The inferior border in this 
radiological study consists of the right ventricle and the left 
ventricle at the apex. In lateral views, the right ventricle is 
seen anteriorly, and the left atrium is visualized posteriorly 
(Fig. 3.60B). 


External sulci 

Internal partitions divide the heart into four chambers 
(i.e., two atria and two ventricles) and produce surface or 
external grooves referred to as sulci. 

■ The coronary sulcus circles the heart, separating the 
atria from the ventricles (Fig. 3.61). As it circles the 
heart, it contains the right coronary artery, the small 
cardiac vein, the coronary sinus, and the circumflex 
branch of the left coronary artery. 

■ The anterior and posterior interventricular sulci 
separate the two ventricles—the anterior interventricu¬ 
lar sulcus is on the anterior surface of the heart and 
contains the anterior interventricular artery and the 
great cardiac vein, and the posterior interventricular 
sulcus is on the diaphragmatic surface of the heart and 
contains the posterior interventricular artery and the 
middle cardiac vein. 



Fig. 3.60 Chest radiographs. A. Standard posteroanterior view of the chest. B. Standard lateral view of the heart. 













Regional anatomy • Mediastinum 


3 


A 



Great cardiac vein 


Coronary sulcus 


Right coronary artery 


Anterior interventricular sulcus 


Small cardiac vein 


Anterior interventricular branch 
of left coronary artery 


B 



Middle cardiac vein 


Small cardiac vein 


Right coronary artery 


Posterior interventricular sulcus 


Posterior interventricular branch 
of right coronary artery 


Great cardiac vein 


Circumflex branch of 
left coronary artery 


Coronary sulcus 


Coronary sinus 


Fig. 3.61 Sulci of the heart. A. Anterior surface of the heart. B. Diaphragmatic surface and base of the heart. 


189 






Thorax 


These sulci are continuous interiorly, just to the right of 
the apex of the heart. 

Cardiac chambers 

The heart functionally consists of two pumps separated by 
a partition (Fig. 3.62A). The right pump receives deoxy- 
genated blood from the body and sends it to the lungs. The 
left pump receives oxygenated blood from the lungs and 
sends it to the body. Each pump consists of an atrium and 
a ventricle separated by a valve. 


The thin-walled atria receive blood coming into the 
heart, whereas the relatively thick-walled ventricles pump 
blood out of the heart. 

More force is required to pump blood through the body 
than through the lungs, so the muscular wall of the left 
ventricle is thicker than the right. 

Interatrial, interventricular, and atrioventricular septa 
separate the four chambers of the heart (Fig. 3.62B). The 
internal anatomy of each chamber is critical to its 
function. 


Superior vena cava 




Fig. 3.62 A. The heart has two pumps. B. Magnetic resonance image of midthorax showing all four chambers and septa. 



















































































Regional anatomy • Mediastinum 


3 


Right atrium 

In the anatomical position, the right border of the heart is 
formed by the right atrium. This chamber also contrib¬ 
utes to the right portion of the heart’s anterior surface. 

Blood returning to the right atrium enters through one 
of three vessels. These are: 

■ the superior and inferior venae cavae, which together 
deliver blood to the heart from the body; and 

■ the coronary sinus, which returns blood from the walls 
of the heart itself. 

The superior vena cava enters the upper posterior 
portion of the right atrium, and the inferior vena cava and 
coronary sinus enter the lower posterior portion of the 
right atrium. 

From the right atrium, blood passes into the right ven¬ 
tricle through the right atrioventricular orifice. This 


opening faces forward and medially and is closed during 
ventricular contraction by the tricuspid valve. 

The interior of the right atrium is divided into two con¬ 
tinuous spaces. Externally, this separation is indicated by a 
shallow, vertical groove (the sulcus terminalis cordis), 
which extends from the right side of the opening of the 
superior vena cava to the right side of the opening of the 
inferior vena cava. Internally, this division is indicated 
by the crista terminalis (Fig. 3.63), which is a smooth, 
muscular ridge that begins on the roof of the atrium just 
in front of the opening of the superior vena cava and 
extends down the lateral wall to the anterior lip of the 
inferior vena cava. 

The space posterior to the crista is the sinus of venae 
cavae and is derived embryologically from the right horn 
of the sinus venosus. This component of the right atrium 
has smooth, thin walls, and both venae cavae empty into 
this space. 



Superior vena cava 


Limbus of fossa ovalis 


Crista terminalis 


Musculi pectinati 


Fossa ovalis 


Inferior vena cava 


Arch of aorta 


Right auricle 


Right ventricle 


Valve of inferior vena cava 


Opening of coronary sinus 


Valve of coronary sinus 


Fig. 3.63 Internal view of right atrium. 


191 












Thorax 


The space anterior to the crista, including the right 
auricle, is sometimes referred to as the atrium proper. 
This terminology is based on its origin from the embryonic 
primitive atrium. Its walls are covered by ridges called the 
musculi pectinati (pectinate muscles), which fan out 
from the crista like the “teeth of a comb.” These ridges 
are also found in the right auricle, which is an ear-like, 
conical, muscular pouch that externally overlaps the 
ascending aorta. 

An additional structure in the right atrium is the 
opening of the coronary sinus, which receives blood 
from most of the cardiac veins and opens medially to the 
opening of the inferior vena cava. Associated with 
these openings are small folds of tissue derived from the 
valve of the embryonic sinus venosus (the valve of the 
coronary sinus and the valve of inferior vena cava, 
respectively). During development, the valve of the inferior 
vena cava helps direct incoming oxygenated blood through 
the foramen ovale and into the left atrium. 

Separating the right atrium from the left atrium is the 
interatrial septum, which faces forward and to the right 
because the left atrium lies posteriorly and to the left of the 
right atrium. A depression is clearly visible in the septum 
just above the orifice of the inferior vena cava. This is the 
fossa ovalis (oval fossa), with its prominent margin, the 
limbus fossa ovalis (border of the oval fossa). 

The fossa ovalis marks the location of the embryonic 
foramen ovale, which is an important part of fetal circu¬ 
lation. The foramen ovale allows oxygenated blood enter¬ 
ing the right atrium through the inferior vena cava to pass 
directly to the left atrium and so bypass the lungs, which 
are nonfunctional before birth. 

Finally, numerous small openings—the openings of 
the smallest cardiac veins (the foramina of the venae 
cordis minimae) —are scattered along the walls of the 
right atrium. These are small veins that drain the myocar¬ 
dium directly into the right atrium. 

Right ventricle 

In the anatomical position, the right ventricle forms most 
of the anterior surface of the heart and a portion of the 
diaphragmatic surface. The right atrium is to the right of 
the right ventricle and the right ventricle is located in front 
of and to the left of the right atrioventricular orifice. Blood 
entering the right ventricle from the right atrium therefore 
moves in a horizontal and forward direction. 

The outflow tract of the right ventricle, which leads to 
the pulmonary trunk, is the conus arteriosus (infun¬ 
dibulum). This area has smooth walls and derives from 
the embryonic bulbus cordis. 

The walls of the inflow portion of the right ventricle 
192 have numerous muscular, irregular structures called 


trabeculae carneae (Fig. 3.64). Most of these are either 
attached to the ventricular walls throughout their length, 
forming ridges, or attached at both ends, forming bridges. 

A few trabeculae carneae (papillary muscles) have 
only one end attached to the ventricular surface, while the 
other end serves as the point of attachment for tendon-like 
fibrous cords (the chordae tendineae), which connect to 
the free edges of the cusps of the tricuspid valve. 

There are three papillary muscles in the right ventricle. 
Named relative to their point of origin on the ventricular 
surface, they are the anterior, posterior, and septal papil¬ 
lary muscles: 

■ The anterior papillary muscle is the largest and most 
constant papillary muscle, and arises from the anterior 
wall of the ventricle. 

■ The posterior papillary muscle may consist of one, 
two, or three structures, with some chordae tendineae 
arising directly from the ventricular wall. 

■ The septal papillary muscle is the most inconsis¬ 
tent papillary muscle, being either small or absent, 
with chordae tendineae emerging directly from the 
septal wall. 

A single specialized trabeculum, the septomarginal 
trabecula (moderator band), forms a bridge between 
the lower portion of the interventricular septum and 
the base of the anterior papillary muscle. The septomar¬ 
ginal trabecula carries a portion of the cardiac conduction 
system, the right bundle of the atrioventricular bundle, to 
the anterior wall of the right ventricle. 

Tricuspid valve 

The right atrioventricular orifice is closed during ventricu¬ 
lar contraction by the tricuspid valve (right atrioven¬ 
tricular valve), so named because it usually consists of 
three cusps or leaflets (Fig. 3.64). The base of each cusp is 
secured to the fibrous ring that surrounds the atrioven¬ 
tricular orifice. This fibrous ring helps to maintain the 
shape of the opening. The cusps are continuous with each 
other near their bases at sites termed commissures. 

The naming of the three cusps, the anterior, septal, 
and posterior cusps, is based on their relative position in 
the right ventricle. The free margins of the cusps are 
attached to the chordae tendineae, which arise from the 
tips of the papillary muscles. 

During filling of the right ventricle, the tricuspid 
valve is open, and the three cusps project into the right 
ventricle. 

Without the presence of a compensating mechanism, 
when the ventricular musculature contracts, the valve 
cusps would be forced upward with the flow of blood and 


Regional anatomy • Mediastinum 


3 



Pulmonary trunk 


Chordae tendineae 


Superior vena cava 


Arch of aorta 


Conus arteriosus 


Right auricle 


Left auricle 


Pulmonary 

valve 


Tricuspid 

valve' 


'Anterior cusp 
Septal cusp 
_ Posterior cusp 


Septal papillary muscle 
Septomarginal trabecula 


Right atrium 


Anterior semilunar cusp — 
Right semilunar cusp 
Left semilunar cusp- 


Anterior papillary muscle 


Posterior papillary muscle 


Trabeculae carneae 


Fig. 3.64 Internal view of the right ventricle. 


blood would move back into the right atrium. However, 
contraction of the papillary muscles attached to the cusps 
by chordae tendineae prevents the cusps from being everted 
into the right atrium. 

Simply put, the papillary muscles and associated 
chordae tendineae keep the valves closed during the 
dramatic changes in ventricular size that occur during 
contraction. 

In addition, chordae tendineae from two papillary 
muscles attach to each cusp. This helps prevent separation 
of the cusps during ventricular contraction. Proper closing 
of the tricuspid valve causes blood to exit the right ventricle 
and move into the pulmonary trunk. 

Necrosis of a papillary muscle following a myocardial 
infarction (heart attack) may result in prolapse of the 
related valve. 

Pulmonary valve 

At the apex of the infundibulum, the outflow tract of the 
right ventricle, the opening into the pulmonary trunk 


is closed by the pulmonary valve (Fig. 3.64), which 
consists of three semilunar cusps with free edges pro¬ 
jecting upward into the lumen of the pulmonary trunk. 
The free superior edge of each cusp has a middle, thick¬ 
ened portion, the nodule of the semilunar cusp, and 
a thin lateral portion, the lunula of the semilunar cusp 
(Fig. 3.65). 

The cusps are named the left, right, and anterior 
semilunar cusps, relative to their fetal position before 
rotation of the outflow tracts from the ventricles is com¬ 
plete. Each cusp forms a pocket-like sinus (Fig. 3.65) —a 
dilation in the wall of the initial portion of the pulmonary 
trunk. After ventricular contraction, the recoil of blood fills 
these pulmonary sinuses and forces the cusps closed. 
This prevents blood in the pulmonary trunk from refilling 
the right ventricle. 


The left atrium forms most of the base or posterior surface 
of the heart. 


Left atrium 


193 

















Thorax 



Nodule 


Pulmonary sinus 


Nodule 


Pulmonary sinus 


Lunule 



Left Anterior Right 
Semilunar cusps 

Fig. 3.65 Posterior view of the pulmonary valve. 


Left ventricle 

The left ventricle lies anterior to the left atrium. It contrib¬ 
utes to the anterior, diaphragmatic, and left pulmonary 
surfaces of the heart, and forms the apex. 

Blood enters the ventricle through the left atrioven¬ 
tricular orifice and flows in a forward direction to the 
apex. The chamber itself is conical, is longer than the right 
ventricle, and has the thickest layer of myocardium. The 
outflow tract (the aortic vestibule) is posterior to the 
infundibulum of the right ventricle, has smooth walls, and 
is derived from the embryonic bulbus cordis. 

The trabeculae carneae in the left ventricle are fine 
and delicate in contrast to those in the right ventricle. 
The general appearance of the trabeculae with muscular 
ridges and bridges is similar to that of the right ventricle 
(Fig. 3.67). 

Papillary muscles, together with chordae tendineae, are 
also observed and their structure is as described above for 
the right ventricle. Two papillary muscles, the anterior 
and posterior papillary muscles, are usually found in 
the left ventricle and are larger than those of the right 
ventricle. 

In the anatomical position, the left ventricle is some¬ 
what posterior to the right ventricle. The interventricular 
septum therefore forms the anterior wall and some of the 
wall on the right side of the left ventricle. The septum is 
described as having two parts: 


As with the right atrium, the left atrium is derived 
embryologically from two structures. 


■ a muscular part, and 

■ a membranous part. 


■ The posterior half, or inflow portion, receives the four 
pulmonary veins (Fig. 3.66). It has smooth walls and 
derives from the proximal parts of the pulmonary veins 
that are incorporated into the left atrium during 
development. 

■ The anterior half is continuous with the left auricle. It 
contains musculi pectinati and derives from the embry¬ 
onic primitive atrium. Unlike the crista terminalis in the 
right atrium, no distinct structure separates the two 
components of the left atrium. 

The interatrial septum is part of the anterior wall of the 
left atrium. The thin area or depression in the septum is 
the valve of the foramen ovale and is opposite the floor of 
the fossa ovalis in the right atrium. 

During development, the valve of the foramen ovale 
prevents blood from passing from the left atrium to the 
right atrium. This valve may not be completely fused in 
some adults, leaving a “probe patent” passage between the 
right atrium and the left atrium. 


The muscular part is thick and forms the major part of 
the septum, whereas the membranous part is the thin, 
upper part of the septum. A third part of the septum may 
be considered an atrioventricular part because of its posi¬ 
tion above the septal cusp of the tricuspid valve. This supe¬ 
rior location places this part of the septum between the left 
ventricle and right atrium. 

Mitral valve 

The left atrioventricular orifice opens into the posterior 
right side of the superior part of the left ventricle. It is 
closed during ventricular contraction by the mitral valve 
(left atrioventricular valve), which is also referred to 
as the bicuspid valve because it has two cusps, the ante¬ 
rior and posterior cusps (Fig. 3.67). The bases of the 
cusps are secured to a fibrous ring surrounding the 
opening, and the cusps are continuous with each other 
at the commissures. The coordinated action of the papil¬ 
lary muscles and chordae tendineae is as described for the 
right ventricle. 


194 










Regional anatomy • Mediastinum 


3 


A 



Arch of aorta 


Left auricle 


Pulmonary veins 


Pulmonary arteries 


Left ventricle 


Valve of foramen ovale 

Left atrium 

Mitral valve 


Ascending aorta 


Right pulmonary vein 
Esophagus 



Right ventricle 


Left atrium 

Left pulmonary vein 


Thoracic aorta 


Fig. 3.66 Left atrium. A. Internal view. B. Axial computed tomography image showing the pulmonary veins entering the left atrium. 


195 



























Thorax 



196 



Arch of aorta 


Mitral valve anterior cusp 


Pulmonary arteries 


Chordae tendineae 


Pulmonary veins 


Anterior papillary 
muscle 


Trabeculae carneae 


Left atrium 


Posterior papillary 
muscle 

Fig. 3.67 Internal view of the left ventricle. 


Coronary sinus 


Mitral valve posterior cusp 


Aortic valve 

The aortic vestibule, or outflow tract of the left ventricle, 
is continuous superiorly with the ascending aorta. The 
opening from the left ventricle into the aorta is closed by 
the aortic valve. This valve is similar in structure to the 
pulmonary valve. It consists of three semilunar cusps 
with the free edge of each projecting upward into the 
lumen of the ascending aorta (Fig. 3.68). 

Between the semilunar cusps and the wall of the 
ascending aorta are pocket-like sinuses—the right, left, 
and posterior aortic sinuses. The right and left coro¬ 
nary arteries originate from the right and left aortic 
sinuses. Because of this, the posterior aortic sinus and 
cusp are sometimes referred to as the noncoronary 
sinus and cusp. 

The functioning of the aortic valve is similar to that of 
the pulmonary valve with one important additional 
process: as blood recoils after ventricular contraction and 
fills the aortic sinuses, it is automatically forced into the 
coronary arteries because these vessels originate from the 
right and left aortic sinuses. 






























Regional anatomy • Mediastinum 


3 


In the clinic 

Valve disease 

Valve problems consist of two basic types: 

■ incompetence (insufficiency), which results from 
poorly functioning valves; and 

■ stenosis, a narrowing of the orifice, caused by the 
valve's inability to open fully. 

Mitral valve disease is usually a mixed pattern of 
stenosis and incompetence, one of which usually 
predominates. Both stenosis and incompetence lead to 
a poorly functioning valve and subsequent heart 
changes, which include: 

■ left ventricular hypertrophy (this is appreciably less 
marked in patients with mitral stenosis); 

■ increased pulmonary venous pressure; 

■ pulmonary edema; and 

■ enlargement (dilation) and hypertrophy of the 
left atrium. 

Aortic valve disease —both aortic stenosis and 
aortic regurgitation (backflow) can produce marked 
heart failure. 

Valve disease in the right side of the heart 
(affecting the tricuspid or pulmonary valve) is most 
likely caused by infection. The resulting valve 
dysfunction produces abnormal pressure changes in the 
right atrium and right ventricle, and these can induce 
cardiac failure. 


Cardiac skeleton 

The cardiac skeleton is a collection of dense, fibrous con¬ 
nective tissue in the form of four rings with interconnect¬ 
ing areas in a plane between the atria and the ventricles. 
The four rings of the cardiac skeleton surround the two 
atrioventricular orifices, the aortic orifice and opening of 
the pulmonary trunks. They are the anulus fibrosus. The 
interconnecting areas include: 

■ the right fibrous trigone, which is a thickened area of 
connective tissue between the aortic ring and right 
atrioventricular ring; and 

■ the left fibrous trigone, which is a thickened area of 
connective tissue between the aortic ring and the left 
atrioventricular ring (Fig. 3.69). 

The cardiac skeleton helps maintain the integrity of the 
openings it surrounds and provides points of attachment 
for the cusps. It also separates the atrial musculature from 
the ventricular musculature. The atrial myocardium origi¬ 
nates from the upper border of the rings, whereas the ven¬ 
tricular myocardium originates from the lower border of 
the rings. 

The cardiac skeleton also serves as a dense connective 
tissue partition that electrically isolates the atria from 



Left fibrous trigone 


Left 


Left atrioventricular ring 


Anterior 

Fibrous ring of pulmonary valve 


Right atrioventricular ring 


Posterior 


Fibrous ring of aortic valve 


Right 


Atrioventricular bundle 


Right fibrous trigone 


Fig. 3.69 Cardiac skeleton (atria removed). 


197 










Thorax 


the ventricles. The atrioventricular bundle, which passes 
through the anulus, is the single connection between these 
two groups of myocardium. 

Coronary vasculature 

Two coronary arteries arise from the aortic sinuses in the 
initial portion of the ascending aorta and supply the 
muscle and other tissues of the heart. They circle the heart 
in the coronary sulcus, with marginal and interventricular 
branches, in the interventricular sulci, converging toward 
the apex of the heart (Fig. 3.70). 

The returning venous blood passes through cardiac 
veins, most of which empty into the coronary sinus. This 
large venous structure is located in the coronary sulcus on 
the posterior surface of the heart between the left atrium 
and left ventricle. The coronary sinus empties into the right 
atrium between the opening of the inferior vena cava and 
the right atrioventricular orifice. 

Coronary arteries 

Right coronary artery. The right coronary artery origi¬ 
nates from the right aortic sinus of the ascending aorta. It 
passes anteriorly and then descends vertically in the coro¬ 
nary sulcus, between the right atrium and right ventricle 
(Fig. 3.71 A). On reaching the inferior margin of the heart, 
it turns posteriorly and continues in the sulcus onto the 
diaphragmatic surface and base of the heart. During this 
course, several branches arise from the main stem of the 
vessel: 

■ An early atrial branch passes in the groove between 
the right auricle and ascending aorta, and gives off 
the sinu-atrial nodal branch (Fig. 3.71 A), which 
passes posteriorly around the superior vena cava to 
supply the sinu-atrial node. 

■ A right marginal branch is given off as the right coro¬ 
nary artery approaches the inferior (acute) margin of 
the heart (Fig. 3.71 A,B) and continues along this border 
toward the apex of the heart. 

■ As the right coronary artery continues on the base/ 
diaphragmatic surface of the heart, it supplies a small 
branch to the atrioventricular node before giving 
off its final major branch, the posterior interventric¬ 
ular branch (Fig. 3.71 A), which lies in the posterior 
interventricular sulcus. 


The right coronary artery supplies the right atrium 
and right ventricle, the sinu-atrial and atrioventricular 
nodes, the interatrial septum, a portion of the left atrium, 
the posteroinferior one third of the interventricular 
septum, and a portion of the posterior part of the left 
ventricle. 

Left coronary artery. The left coronary artery originates 
from the left aortic sinus of the ascending aorta. It passes 
between the pulmonary trunk and the left auricle before 
entering the coronary sulcus. Emerging from behind the 
pulmonary trunk, the artery divides into its two terminal 
branches, the anterior interventricular and the circumflex 
(Fig. 3.71A). 

■ The anterior interventricular branch (left ante¬ 
rior descending artery—LAD) (Fig. 3.71A,C) contin¬ 
ues around the left side of the pulmonary trunk and 
descends obliquely toward the apex of the heart in the 
anterior interventricular sulcus (Fig. 3.71A,C). During 
its course, one or two large diagonal branches may 
arise and descend diagonally across the anterior surface 
of the left ventricle. 

■ The circumflex branch (Fig. 3.71 A,C) courses toward 
the left, in the coronary sulcus and onto the base/ 
diaphragmatic surface of the heart, and usually ends 
before reaching the posterior interventricular sulcus. A 
large branch, the left marginal artery (Fig. 3.71A,C), 
usually arises from it and continues across the rounded 
obtuse margin of the heart. 

The distribution pattern of the left coronary artery 
enables it to supply most of the left atrium and left ventri¬ 
cle, and most of the interventricular septum, including the 
atrioventricular bundle and its branches. 

Variations in the distribution patterns of coronary arter¬ 
ies. Several major variations in the basic distribution pat¬ 
terns of the coronary arteries occur. 

■ The distribution pattern described above for both right 
and left coronary arteries is the most common and con¬ 
sists of a right dominant coronary artery. This means 
that the posterior interventricular branch arises from 
the right coronary artery. The right coronary artery 
therefore supplies a large portion of the posterior wall 
of the left ventricle and the circumflex branch of the left 
coronary artery is relatively small. 


198 


Regional anatomy • Mediastinum 


3 


A 



Ascending aorta 


Anterior interventricular 
branches 


Marginal branches 


Coronary sulcus 


Marginal branches 


Posterior interventricular 
branches 


Apex 



Aortic sinuses 


Coronary si 


Coronary sulcus 


Right atrioventricular 
opening 


Left 


Right 


B 


Posterior 


Fig. 3.70 Cardiac vasculature. A. Anterior view. B. Superior view (atria removed). 


199 





















Thorax 




Left coronary artery 


Left ventricle 


Diagonal branch of 
anterior interventricular branch 


Sinu-atrial nodal branch 
of right coronary artery 


Left auricle 


Circumflex branch 
of left coronary artery 


Right coronary artery 


Right atrium 


Left marginal branch 
of circumflex branch 


Right ventricle 


Anterior interventricular 
branch of left 
coronary artery 


Right marginal branch 
of right coronary artery 


Posterior interventricular 
branch of right coronary artery 




-Right marginal branch 

200 Fig. 1.71 A. Anterior view of coronary arterial system. Right dominant coronary artery. B. Left anterior oblique view of right coronary 
artery. C. Right anterior oblique view of left coronary artery. 


















Regional anatomy • Mediastinum 


3 



Left coronary artery 


Left marginal branch 
of circumflex branch 


Diagonal branch of 
anterior interventricular branch 


Sinu-atrial nodal branch 
of left coronary artery 


Circumflex branch 
of left coronary artery 


Right coronary artery 


Anterior interventricular 
branch of left coronary artery 


Right marginal branch 
of right coronary artery 


Posterior interventricular branch of 
circumflex branch of left coronary artery 


Fig. 3.72 Left dominant coronary artery. 


In contrast, in hearts with a left dominant coronary 
artery, the posterior interventricular branch arises 
from an enlarged circumflex branch and supplies 
most of the posterior wall of the left ventricle 
(Fig. 3.72). 

Another point of variation relates to the arterial supply 
to the sinu-atrial and atrioventricular nodes. In most 
cases, these two structures are supplied by the right 
coronary artery. However, vessels from the circumflex 
branch of the left coronary artery occasionally supply 
these structures. 


In the clinic 

Clinical terminology for coronary arteries 

In practice, physicians use alternative names for the 
coronary vessels. The short left coronary artery is 
referred to as the left main stem vessel. One of its 
primary branches, the anterior interventricular artery, is 
termed the left anterior descending artery (LAD). 
Similarly, the terminal branch of the right coronary 
artery, the posterior interventricular artery, is termed 
the posterior descending artery (PDA). 


201 










Thorax 


In the clinic 


Heart attack 

A heart attack occurs when the perfusion to the 
myocardium is insufficient to meet the metabolic needs 
of the tissue, leading to irreversible tissue damage. The 
most common cause is a total occlusion of a major 
coronary artery. 

Coronary Artery Disease 

Occlusion of a major coronary artery, usually due to 
atherosclerosis, leads to inadequate oxygenation of an 
area of myocardium and cell death (Fig. 3.73). The severity 
of the problem will be related to the size and location of 
the artery involved, whether or not the blockage is 
complete, and whether there are collateral vessels to 
provide perfusion to the territory from other vessels. 
Depending on the severity, patients can develop pain 
(angina) or a myocardial infarction (Ml). 

Percutaneous Coronary Intervention 

This is a technique in which a long fine tube (a catheter) is 
inserted into the femoral artery in the thigh and passed 
through the external and common iliac arteries and into 


the abdominal aorta. It continues to be moved upward 
through the thoracic aorta to the origins of the coronary 
arteries. The coronaries may also be approached via the 
radial or brachial arteries. A fine wire is then passed into 
the coronary artery and is used to cross the stenosis. A 
fine balloon is then passed over the wire and may be 
inflated at the level of the obstruction, thus widening it; 
this is termed angioplasty. More commonly, this is 
augmented by placement of a fine wire mesh (a stent) 
inside the obstruction to hold it open. Other percutaneous 
interventions are suction extraction of a coronary 
thrombus and rotary ablation of a plaque. 

Coronary Artery Bypass Grafts 

If coronary artery disease is too extensive to be treated 
by percutaneous intervention, surgical coronary artery 
bypass grafting may be necessary. The great saphenous 
vein, in the lower limb, is harvested and used as a graft. 

It is divided into several pieces, each of which is used to 
bypass blocked sections of the coronary arteries. The 
internal thoracic and radial arteries can also be used. 



Anterior- 
interventricular 
artery 




Fig. 3.73 A and B. Axial maximum intensity projection (MIP) CT image through the heart. A. Normal anterior interventricular (left 
anterior descending) artery. B. Stenotic (calcified) anterior interventricular (left anterior descending) artery. C and D. Vertical long 
axis multiplanar reformation (MRP) CT image through the heart. C. Normal anterior interventricular (left anterior descending) artery. 
D. Stenotic (calcified) anterior interventricular (left anterior descending) artery. 


202 



Regional anatomy • Mediastinum 


3 


In the clinic 

Classic symptoms of heart attack 

The typical symptoms are chest heaviness or pressure, 
which can be severe, lasting more than 20 minutes, and 
often associated with sweating. The pain in the chest 
(which may be described as an "elephant sitting on my 
chest" or by using a clenched fist to describe the pain 
[Levine sign]) often radiates to the arms (left more 
common than the right), and can be associated with 
nausea. The severity of ischemia and infarction depends 
on the rate at which the occlusion or stenosis has 
occurred and whether or not collateral channels have 
had a chance to develop. 


In the clinic 

Are heart attack symptoms the same in men 
and women? 

Although men and women can experience the typical 
symptoms of severe chest pain, cold sweats, and pain in 
the left arm, women are more likely than men to have 
subtler, less recognizable symptoms. These may include 
abdominal pain, achiness in the jaw or back, nausea, 
shortness of breath, or simply fatigue. The mechanism 
of this difference is not understood, but it is important 
to consider cardiac ischemia for a wide range of 
symptoms. 


In the clinic 

Common congenital heart defects 

The most common abnormalities that occur during 
development are those produced by a defect in the 
atrial and ventricular septa. 

A defect in the interatrial septum allows blood to 
pass from one side of the heart to the other from the 
chamber with the higher pressure; this is clinically referred 
to as a shunt. An atrial septal defect (ASD) allows 
oxygenated blood to flow from the left atrium (higher 
pressure) across the ASD into the right atrium (lower 
pressure). Many patients with ASD are asymptomatic, but 
in some cases the ASD may need to be closed surgically or 
by endovascular devices. Occasionally, increased blood 
flow into the right atrium over many years leads to right 
atrial and right ventricular hypertrophy and enlargement 
of the pulmonary trunk, resulting in pulmonary arterial 
hypertension. 

The most common of all congenital heart defects 
are those that occur in the ventricular septum— 
ventriculoseptal defect (VSD). These lesions are most 
frequent in the membranous portion of the septum and 
they allow blood to move from the left ventricle (higher 
pressure) to the right ventricle (lower pressure); this leads 


to right ventricular hypertrophy and pulmonary arterial 
hypertension. If large enough and left untreated, VSDs 
can produce marked clinical problems that might 
require surgery. 

Occasionally, the ductus arteriosus, which connects 
the left branch of the pulmonary artery to the inferior 
aspect of the aortic arch, fails to close at birth. When this 
occurs, the oxygenated blood in the aortic arch (higher 
pressure) passes into the left branch of the pulmonary 
artery (lower pressure) and produces pulmonary 
hypertension. This is termed a patent or persistent 
ductus arteriosus (PDA). 

All of these defects produce a left-to-right shunt, 
indicating that oxygenated blood from the left heart is 
being mixed with deoxygenated blood from the right 
heart before being recirculated into the pulmonary 
circulation. These shunts are normally compatible with 
life, but surgery or endovascular treatment may be 
necessary. 

Rarely, a shunt is right-to-left. In isolation this is fatal; 
however, this type of shunt is often associated with other 
anomalies, so some deoxygenated blood is returned to 
the lungs and the systemic circulation. 


203 



Thorax 


In the clinic 
Cardiac auscultation 

Auscultation of the heart reveals the normal audible 
cardiac cycle, which allows the clinician to assess heart 
rate, rhythm, and regularity. Furthermore, cardiac 
murmurs that have characteristic sounds within the 
phases of the cardiac cycle can be demonstrated 
(Fig. 3.74). 



Closure of mitral Closure of aortic and 
and tricuspid valves pulmonary valves 


Ventricular 

pressure 



Heart 

sounds 



"lub" 


"dub" 


"lub" 


♦ SYSTOLE* *—DIASTOLE—► *SYSTOLE* 


Fig. 3.74 Heart sounds and how they relate to valve closure, 
the electrocardiogram (ECG), and ventricular pressure. 


Cardiac veins 

The coronary sinus receives four major tributaries: the 
great, middle, small, and posterior cardiac veins. 

Great cardiac vein. The great cardiac vein begins at 
the apex of the heart (Fig. 3.75A). It ascends in the ante¬ 
rior interventricular sulcus, where it is related to the ante¬ 
rior interventricular artery and is often termed the anterior 
interventricular vein. Reaching the coronary sulcus, the 
great cardiac vein turns to the left and continues onto the 
base/diaphragmatic surface of the heart. At this point, it is 
associated with the circumflex branch of the left coronary 
artery. Continuing along its path in the coronary sulcus, 
the great cardiac vein gradually enlarges to form the coro- 
204 nary sinus, which enters the right atrium (Fig. 3.75B). 


Middle cardiac vein. The middle cardiac vein (posterior 
interventricular vein) begins near the apex of the heart 
and ascends in the posterior interventricular sulcus toward 
the coronary sinus (Fig. 3.75B). It is associated with the 
posterior interventricular branch of the right or left coro¬ 
nary artery throughout its course. 

Small cardiac vein. The small cardiac vein begins in the 
lower anterior section of the coronary sulcus between the 
right atrium and right ventricle (Fig. 3.75A). It continues 
in this groove onto the base/diaphragmatic surface of the 
heart where it enters the coronary sinus at its atrial end. 
It is a companion of the right coronary artery throughout 
its course and may receive the right marginal vein (Fig. 
3.75 A). This small vein accompanies the marginal branch 
of the right coronary artery along the acute margin of the 
heart. If the right marginal vein does not join the small 
cardiac vein, it enters the right atrium directly. 

Posterior cardiac vein. The posterior cardiac vein lies on 
the posterior surface of the left ventricle just to the left of 
the middle cardiac vein (Fig. 3.75B). It either enters the 
coronary sinus directly or joins the great cardiac vein. 

Other cardiac veins. Two additional groups of cardiac 
veins are also involved in the venous drainage of the 
heart. 

■ The anterior veins of the right ventricle (anterior 
cardiac veins) are small veins that arise on the anterior 
surface of the right ventricle (Fig. 3.75A). They cross 
the coronary sulcus and enter the anterior wall of the 
right atrium. They drain the anterior portion of the 
right ventricle. The right marginal vein may be part 
of this group if it does not enter the small cardiac 
vein. 

■ A group of smallest cardiac veins (venae cordis 
minimae or veins of Thebesius) have also been 
described. Draining directly into the cardiac chambers, 
they are numerous in the right atrium and right ven¬ 
tricle, are occasionally associated with the left atrium, 
and are rarely associated with the left ventricle. 


Coronary lymphatics 

The lymphatic vessels of the heart follow the coronary 
arteries and drain mainly into: 

■ brachiocephalic nodes, anterior to the brachiocephalic 
veins; and 

■ tracheobronchial nodes, at the inferior end of the 
trachea. 










Regional anatomy • Mediastinum 


3 



Small cardiac vein 


Great cardiac vein 


Anterior veins 
of right ventricle 


A Right marginal vein 


Great cardiac vein 


Posterior cardiac vein 


Coronary sinus 


Fig. 3.75 Major cardiac veins. A. Anterior view of major cardiac veins. 


Coronary sinus 


Anterior interventricular vein 


Small cardiac vein 


Middle cardiac vein 


B. Posteroinferior view of major cardiac veins. 


Middle cardiac vein 


205 


















Thorax 


Cardiac conduction system 

The musculature of the atria and ventricles is capable of 
contracting spontaneously. The cardiac conduction system 
initiates and coordinates contraction. The conduction 
system consists of nodes and networks of specialized 
cardiac muscle cells organized into four basic components: 

■ the sinu-atrial node, 

■ the atrioventricular node, 

■ the atrioventricular bundle with its right and left bundle 
branches, and 

■ the subendocardial plexus of conduction cells (the Pur- 
kin je fibers). 

The unique distribution pattern of the cardiac conduc¬ 
tion system establishes an important unidirectional 
pathway of excitation/contraction. Throughout its course, 
large branches of the conduction system are insulated 
from the surrounding myocardium by connective tissue. 
This tends to decrease inappropriate stimulation and con¬ 
traction of cardiac muscle fibers. 

The number of functional contacts between the con¬ 
duction pathway and cardiac musculature greatly in¬ 
creases in the subendocardial network. 

Thus, a unidirectional wave of excitation and contrac¬ 
tion is established, which moves from the papillary muscles 
and apex of the ventricles to the arterial outflow tracts. 

In the clinic 

Cardiac conduction system 

The cardiac conduction system can be affected by 
coronary artery disease. The normal rhythm may be 
disturbed if the blood supply to the coronary 
conduction system is disrupted. If a dysrhythmia affects 
the heart rate or the order in which the chambers 
contract, heart failure and death may ensue. 

Sinu-atrial node 

Impulses begin at the sinu-atrial node, the cardiac 
pacemaker. This collection of cells is located at the supe¬ 
rior end of the crista terminalis at the junction of the 
superior vena cava and the right atrium (Fig. 3.76A). 
This is also the junction between the parts of the right 
atrium derived from the embryonic sinus venosus and the 
atrium proper. 


The excitation signals generated by the sinu-atrial node 
spread across the atria, causing the muscle to contract. 

Atrioventricular node 

Concurrently, the wave of excitation in the atria stimulates 
the atrioventricular node, which is located near the 
opening of the coronary sinus, close to the attachment of 
the septal cusp of the tricuspid valve, and within the atrio¬ 
ventricular septum (Fig. 3.76A). 

The atrioventricular node is a collection of specialized 
cells that forms the beginning of an elaborate system of 
conducting tissue, the atrioventricular bundle, which 
extends the excitatory impulse to all ventricular 
musculature. 

Atrioventricular bundle 

The atrioventricular bundle is a direct continuation 
of the atrioventricular node (Fig. 3.76A). It follows 
along the lower border of the membranous part of the 
interventricular septum before splitting into right and left 
bundles. 

The right bundle branch continues on the right side 
of the interventricular septum toward the apex of the right 
ventricle. From the septum it enters the septomarginal tra¬ 
becula to reach the base of the anterior papillary muscle. 
At this point, it divides and is continuous with the final 
component of the cardiac conduction system, the suben¬ 
docardial plexus of ventricular conduction cells or Pur- 
kinje fibers. This network of specialized cells spreads 
throughout the ventricle to supply the ventricular muscu¬ 
lature, including the papillary muscles. 

The left bundle branch passes to the left side of the 
muscular interventricular septum and descends to the 
apex of the left ventricle (Fig. 3.76B). Along its course 
it gives off branches that eventually become continuous 
with the subendocardial plexus of conduction cells 
(Purkinje fibers). As with the right side, this network of 
specialized cells spreads the excitation impulses through¬ 
out the left ventricle. 

Cardiac innervation 

The autonomic division of the peripheral nervous system 
is directly responsible for regulating: 

■ heart rate, 

■ force of each contraction, and 

■ cardiac output. 


206 


Regional anatomy • Mediastinum 


3 



Superior vena cava 


Atrioventricular bundle 
Atrioventricular node 


Left bundle 


Sinu-atrial node 


Right bundle branch 


Septomarginal 

trabecula 


Left ventricle 


Aorta 


Pulmonary trunk 


Right pulmonary 
veins 


Left atrium 


Posterior papillary 
muscle 


Inferior vena cava 


Right ventricle 
Anterior papillary muscle 

Aorta 

Pulmonary trunk 


Anterior papillary 
muscle 


Fig. 3.76 Conduction system of the heart. A. Right chambers. B. Left chambers. 


207 



























Thorax 


Branches from both the parasympathetic and sympa¬ 
thetic systems contribute to the formation of the cardiac 
plexus. This plexus consists of a superficial part, inferior 
to the aortic arch and between it and the pulmonary trunk 
(Fig. 3.77A), and a deep part, between the aortic arch and 
the tracheal bifurcation (Fig. 3.77B). 


From the cardiac plexus, small branches that are 
mixed nerves containing both sympathetic and parasym¬ 
pathetic fibers supply the heart. These branches affect 
nodal tissue and other components of the conduction 
system, coronary blood vessels, and atrial and ventricular 
musculature. 


A 



nerves from 
sympathetic trunk 


Right vagus nerve 
Vagal cardiac branches 

Arch of aorta 
Superior vena cava 


Left vagus nerve 


Vagal cardiac branches 

Superficial cardiac plexus 


Pulmonary trunk 


Cardiac nerves from sympathetic trunk 



208 


Fig. 3.77 Cardiac plexus. A. Superficial. B. Deep. 


















































Regional anatomy • Mediastinum 


3 


Parasympathetic innervation 

Stimulation of the parasympathetic system: 

■ decreases heart rate, 

■ reduces force of contraction, and 

■ constricts the coronary arteries. 

The preganglionic parasympathetic fibers reach the 
heart as cardiac branches from the right and left vagus 
nerves. They enter the cardiac plexus and synapse in 
ganglia located either within the plexus or in the walls of 
the atria. 

Sympathetic innervation 

Stimulation of the sympathetic system: 

■ increases heart rate, and 

■ increases the force of contraction. 

Sympathetic fibers reach the cardiac plexus through the 
cardiac nerves from the sympathetic trunk. Preganglionic 
sympathetic fibers from the upper four or five segments 
of the thoracic spinal cord enter and move through the 
sympathetic trunk. They synapse in cervical and upper 
thoracic sympathetic ganglia, and postganglionic fibers 
proceed as bilateral branches from the sympathetic trunk 
to the cardiac plexus. 


Visceral afferents 

Visceral afferents from the heart are also a component of 
the cardiac plexus. These fibers pass through the cardiac 
plexus and return to the central nervous system in the 
cardiac nerves from the sympathetic trunk and in the vagal 
cardiac branches. 

The afferents associated with the vagal cardiac nerves 
return to the vagus nerve [X]. They sense alterations in 
blood pressure and blood chemistry and are therefore pri¬ 
marily concerned with cardiac reflexes. 

The afferents associated with the cardiac nerves from 
the sympathetic trunks return to either the cervical or the 
thoracic portions of the sympathetic trunk. If they are in 
the cervical portion of the trunk, they normally descend to 
the thoracic region, where they reenter the upper four or 
five thoracic spinal cord segments, along with the afferents 
from the thoracic region of the sympathetic trunk. Visceral 
afferents associated with the sympathetic system conduct 
pain sensation from the heart, which is detected at the 
cellular level as tissue-damaging events (i.e., cardiac 
ischemia). This pain is often “referred” to cutaneous 
regions supplied by the same spinal cord levels (see “In the 
clinic: Referred pain.” p. 48, and “Case 4,” pp. 243-245). 

Pulmonary trunk 

The pulmonary trunk is contained within the pericardial 
sac (Fig. 3.78), is covered by the visceral layer of serous 




Right atrium 


Inferior vena cava 


Oblique pericardial sinus 

B 


Pulmonary trunk Arch of aorta 


Left pulmonary 
artery 


Ascending 

aorta 


Superior 


vena cava 


Left pulmonary— 


Superior vena cava 

Right pulmonary 
artery 


-Right pulmonary 
veins 


Fig. 3.78 Major vessels within the middle mediastinum. A. Anterior view. B. Posterior view. 


209 







Thorax 


pericardium, and is associated with the ascending aorta in 
a common sheath. It arises from the conus arteriosus of 
the right ventricle at the opening of the pulmonary trunk 
slightly anterior to the aortic orifice and ascends, moving 
posteriorly and to the left, lying initially anterior and then 
to the left of the ascending aorta. At approximately the 
level of the intervertebral disc between vertebrae TV and 
TVI, opposite the left border of the sternum and posterior 
to the third left costal cartilage, the pulmonary trunk 
divides into: 

■ the right pulmonary artery, which passes to the right, 
posterior to the ascending aorta and the superior vena 
cava, to enter the right lung; and 

■ the left pulmonary artery, which passes inferiorly to the 
arch of the aorta and anteriorly to the descending aorta 
to enter the left lung. 

Ascending aorta 

The ascending aorta is contained within the pericardial 
sac and is covered by a visceral layer of serous pericardium, 
which also surrounds the pulmonary trunk in a common 
sheath (Fig. 3.78A). 

The origin of the ascending aorta is the aortic orifice at 
the base of the left ventricle, which is level with the lower 
edge of the third left costal cartilage, posterior to the left 
half of the sternum. Moving superiorly, slightly forward 
and to the right, the ascending aorta continues to the level 
of the second right costal cartilage. At this point, it enters 
the superior mediastinum and is then referred to as the 
arch of the aorta. 

Immediately superior to the point where the ascending 
aorta arises from the left ventricle are three small outward 
bulges opposite the semilunar cusps of the aortic valve. 
These are the posterior, right, and left aortic sinuses. The 
right and left coronary arteries originate from the right 
and left aortic sinuses, respectively. 

Other vasculature 

The inferior half of the superior vena cava is located 
within the pericardial sac (Fig. 3.78B). It passes through 
the fibrous pericardium at approximately the level of 
the second costal cartilage and enters the right atrium 
at the lower level of the third costal cartilage. The 
portion within the pericardial sac is covered with serous 
pericardium except for a small area on its posterior 
surface. 

After passing through the diaphragm, at approximately 
the level of vertebra TVIII, the inferior vena cava enters 
the fibrous pericardium. A short portion of this vessel is 


within the pericardial sac before entering the right atrium. 
While within the pericardial sac, it is covered by serous 
pericardium except for a small portion of its posterior 
surface (Fig. 3.78B). 

A very short segment of each of the pulmonary veins is 
also within the pericardial sac. These veins, usually two 
from each lung, pass through the fibrous pericardium and 
enter the superior region of the left atrium on its posterior 
surface. In the pericardial sac, all but a portion of the pos¬ 
terior surface of these veins is covered by serous pericar¬ 
dium. In addition, the oblique pericardial sinus is 
between the right and left pulmonary veins, within the 
pericardial sac (Fig. 3.78B). 

Superior mediastinum 

The superior mediastinum is posterior to the manu¬ 
brium of the sternum and anterior to the bodies of the first 
four thoracic vertebrae (see Fig. 3.52). 

■ Its superior boundary is an oblique plane passing from 
the jugular notch upward and posteriorly to the supe¬ 
rior border of vertebra TI. 

■ Inferiorly, a transverse plane passing from the sternal 
angle to the intervertebral disc between vertebra TIV/V 
separates it from the inferior mediastinum. 

■ Laterally, it is bordered by the mediastinal part of the 
parietal pleura on either side. 

The superior mediastinum is continuous with the neck 
above and with the inferior mediastinum below. 

The major structures found in the superior mediasti¬ 
num (Figs. 3.79 and 3.80) include the: 

■ thymus, 

■ right and left brachiocephalic veins, 

■ left superior intercostal vein, 

■ superior vena cava, 

■ arch of the aorta with its three large branches, 

■ trachea, 

■ esophagus, 

■ phrenic nerves, 

■ vagus nerves, 

■ left recurrent laryngeal branch of the left vagus nerve, 

■ thoracic duct, and 

■ other small nerves, blood vessels, and lymphatics. 

Thymus 

The thymus is the most anterior component of the supe¬ 
rior mediastinum, lying immediately posterior to the 


210 


Regional anatomy • Mediastinum 


3 


Trachea 



Right common carotid 
Right internal jugular vein 

Right subclavian artery 
Right subclavian vein 


Esophagus 

Left common carotid artery 

Left internal jugular vein 

Left subclavian artery 

Left subclavian vein 


Right main bronchus 

Fig. 3.79 Structures in the superior mediastinum. 


Esophagus 


Left brachiocephalic vein 
Arch of aorta 
Left pulmonary artery 
Left main bronchus 
Pulmonary trunk 
Thoracic aorta 

Ascending aorta 


Right brachiocephalic vein 

Right pulmonary artery 


Superior vena cava 


Brachiocephalic trunk 


Thymus 

Right brachiocephalic vein 


Manubrium of sternum 

Left brachiocephalic vein 



Left common 
carotid artery 


subclavian 
artery 


Right phrenic nerve 


Left phrenic nerve 


Trachea 


vagus nerve 


Left recurrent 
laryngeal nerve 


Right vagus nerve 


A 


Esophagus 


Thoracic duct 



Brachiocephalic trunk 


Right brachiocephalic vein 


Left brachiocephalic vein 


Trachea 

Esophagus 


Left subclavian artery 
Left common carotid artery 


Fig. 3.80 Cross section through the superior mediastinum at the level of vertebra Till. A. Diagram. B. Axial computed tomography image. 


211 














































Thorax 


manubrium of the sternum. It is an asymmetrical, bilobed 
structure (Fig. 3.81). 

The upper extent of the thymus can reach into the 
neck as high as the thyroid gland; a lower portion 
typically extends into the anterior mediastinum over the 
pericardial sac. 

Involved in the early development of the immune 
system, the thymus is a large structure in the child, begins 
to atrophy after puberty, and shows considerable size varia¬ 
tion in the adult. In the elderly adult, it is barely identifiable 
as an organ, consisting mostly of fatty tissue that is some¬ 
times arranged as two lobulated fatty structures. 

Arteries to the thymus consist of small branches origi¬ 
nating from the internal thoracic arteries. Venous drain¬ 
age is usually into the left brachiocephalic vein and possibly 
into the internal thoracic veins. 


Lymphatic drainage returns to multiple groups of nodes 
at one or more of the following locations: 

■ along the internal thoracic arteries (parasternal); 

■ at the tracheal bifurcation (tracheobronchial); and 

■ in the root of the neck. 

In the clinic 

Ectopic parathyroid glands in the thymus 

The parathyroid glands develop from the third 
pharyngeal pouch, which also forms the thymus. The 
thymus is therefore a common site for ectopic 
parathyroid glands and, potentially, ectopic parathyroid 
hormone production. 



Left internal thoracic artery 


TIV/V vertebral level 


Pericardial sac 


Right internal thoracic artery 


Thymus 


Fig. 3.81 Thymus. 














Regional anatomy • Mediastinum 


3 


Right and left brachiocephalic veins 

The left and right brachiocephalic veins are located imme¬ 
diately posterior to the thymus. They form on each side at 
the junction between the internal jugular and subclavian 
veins (see Fig. 3.79). The left brachiocephalic vein crosses 
the midline and joins with the right brachiocephalic vein 
to form the superior vena cava (Fig. 3.82). 

■ The right brachiocephalic vein begins posterior to 
the medial end of the right clavicle and passes vertically 
downward, forming the superior vena cava when it is 
joined by the left brachiocephalic vein. Venous tributar¬ 
ies include the vertebral, first posterior intercostal, and 
internal thoracic veins. The inferior thyroid and thymic 
veins may also drain into it. 


■ The left brachiocephalic vein begins posterior to the 
medial end of the left clavicle. It crosses to the right, 
moving in a slightly inferior direction, and joins with the 
right brachiocephalic vein to form the superior vena 
cava posterior to the lower edge of the right first costal 
cartilage close to the right sternal border. Venous tribu¬ 
taries include the vertebral, first posterior intercostal, 
left superior intercostal, inferior thyroid, and internal 
thoracic veins. It may also receive thymic and pericar¬ 
dial veins. The left brachiocephalic vein crosses the 
midline posterior to the manubrium in the adult. In 
infants and children the left brachiocephalic vein rises 
above the superior border of the manubrium and there¬ 
fore is less protected. 


Right vagus nerve 
Right brachiocephalic vein 


Azygos vein 
Superior vena cava 



Left common carotid artery 


Left brachiocephalic vein 
Left vagus nerve 


Left pulmonary artery 


—Left pulmonary veins 


Fig. 3.82 Superior mediastinum with thymus removed. 


213 














Thorax 


Left superior intercostal vein 

The left superior intercostal vein receives the second, 
third, and sometimes the fourth posterior intercostal 
veins, usually the left bronchial veins, and sometimes the 
left pericardiacophrenic vein. It passes over the left side 


of the aortic arch, lateral to the left vagus nerve and 
medial to the left phrenic nerve, before entering the left 
brachiocephalic vein (Fig. 3.83). Interiorly, it may connect 
with the accessory hemiazygos vein (superior hemia¬ 
zygos vein). 



Esophagus 


Left brachiocephalic vein 

Left phrenic nerve 

Left vagus nerve 


Rib I 

Left subclavian artery 


Left superior intercostal vein 


Accessory hemiazygos vein 


Thoracic aorta 


Diaphragm 


Fig. 3.83 Left superior intercostal vein. 


214 

















Regional anatomy • Mediastinum 


3 


Superior vena cava 

The vertically oriented superior vena cava begins posterior 
to the lower edge of the right first costal cartilage, where 
the right and left brachiocephalic veins join, and termi¬ 
nates at the lower edge of the right third costal cartilage, 
where it joins the right atrium (see Fig. 3.79). 

The lower half of the superior vena cava is within the 
pericardial sac and is therefore contained in the middle 
mediastinum. 

The superior vena cava receives the azygos vein imme¬ 
diately before entering the pericardial sac and may also 
receive pericardial and mediastinal veins. 

The superior vena cava can be easily visualized forming 
part of the right superolateral border of the mediastinum 
on a chest radiograph (see Fig. 3.60A). 


In the clinic 

Venous access for central and dialysis lines 

Large systemic veins are used to establish central 
venous access for administering large amounts of fluid, 
drugs, and blood. Most of these lines (small-bore tubes) 
are introduced through venous puncture into the 
axillary, subclavian, or internal jugular veins. The lines 
are then passed through the main veins of the superior 
mediastinum, with the tips of the lines usually residing 
in the distal portion of the superior vena cava or in the 
right atrium. 

Similar devices, such as dialysis lines, are inserted 
into patients who have renal failure, so that a large 
volume of blood can be aspirated through one channel 
and reinfused through a second channel. 


In the clinic 

Using the superior vena cava to access the inferior 
vena cava 

Because the superior and inferior venae cavae are 
oriented along the same vertical axis, a guidewire, 
catheter, or line can be passed from the superior vena 
cava through the right atrium and into the inferior vena 
cava. This is a common route of access for such 
procedures as: 

■ transjugular liver biopsy, 

■ transjugular intrahepatic portosystemic shunts 
(TIPS), and 

■ insertion of an inferior vena cava filter to catch 
emboli dislodged from veins in the lower limb 
and pelvis (i.e., patients with deep vein 
thrombosis [DVT]). 


Arch of aorta and its branches 

The thoracic portion of the aorta can be divided into 
ascending aorta, arch of the aorta, and thoracic 
(descending) aorta. Only the arch of the aorta is in the 
superior mediastinum. It begins when the ascending aorta 
emerges from the pericardial sac and courses upward, 
backward, and to the left as it passes through the superior 
mediastinum, ending on the left side at vertebral level 
TIV/V (see Fig. 3.79). Extending as high as the midlevel of 
the manubrium of the sternum, the arch is initially ante¬ 
rior and finally lateral to the trachea. 

Three branches arise from the superior border of the 
arch of the aorta; at their origins, all three are crossed 
anteriorly by the left brachiocephalic vein. 


215 



Thorax 


The first branch 

Beginning on the right, the first branch of the arch of the 
aorta is the brachiocephalic trunk (Fig. 3.84). It is the 
largest of the three branches and, at its point of origin 
behind the manubrium of the sternum, is slightly anterior 
to the other two branches. It ascends slightly posteriorly 
and to the right. At the level of the upper edge of the right 
sternoclavicular joint, the brachiocephalic trunk divides 
into: 

■ the right common carotid artery, and 

■ the right subclavian artery (see Fig. 3.79). 

The arteries mainly supply the right side of the head and 
neck and the right upper limb, respectively. 

Occasionally, the brachiocephalic trunk has a small 
branch, the thyroid ima artery, which contributes to the 
vascular supply of the thyroid gland. 

The second branch 

The second branch of the arch of the aorta is the left 
common carotid artery (Fig. 3.84). It arises from the 
arch immediately to the left and slightly posterior to the 


brachiocephalic trunk and ascends through the superior 
mediastinum along the left side of the trachea. 

The left common carotid artery supplies the left side of 
the head and neck. 

The third branch 

The third branch of the arch of the aorta is the left sub¬ 
clavian artery (Fig. 3.84). It arises from the arch of the 
aorta immediately to the left of, and slightly posterior to, 
the left common carotid artery and ascends through the 
superior mediastinum along the left side of the trachea. 

The left subclavian artery is the major blood supply to 
the left upper limb. 

Ligamentum arteriosum 

The ligamentum arteriosum is also in the superior 
mediastinum and is important in embryonic circulation, 
when it is a patent vessel (the ductus arteriosus). It con¬ 
nects the pulmonary trunk with the arch of the aorta and 
allows blood to bypass the lungs during development 
(Fig. 3.84). The vessel closes soon afterbirth and forms the 
ligamentous connection observed in the adult. 



Right recurrent laryngeal nerve 
Right common carotid artery 

Right subclavian artery 

Brachiocephalic trunk 

Right vagus nerve 

Superior vena cava 

Ascending aorta 
Right pulmonary artery 


Right pulmonary veins 


Trachea 

Left recurrent laryngeal nerve 

Left common carotid artery 

subclavian artery 


Left vagus nerve 

Ligamentum arteriosum 


1 ~*t pulmonary artery 


Left pulmonary veins 


216 


Fig. 3.84 Superior mediastinum with thymus and venous channels removed. 























Regional anatomy • Mediastinum 


3 


In the clinic 

Coarctation of the aorta 

Coarctation of the aorta is a congenital abnormality in 
which the aortic lumen is constricted just distal to the 
origin of the left subclavian artery. At this point, the 
aorta becomes significantly narrowed and the blood 
supply to the lower limbs and abdomen is diminished. 
Over time, collateral vessels develop around the chest 
wall and abdomen to supply the lower body. The 
coarctation also affects the heart, which has to pump 
the blood at higher pressure to maintain peripheral 
perfusion. This in turn may produce cardiac failure. 


In the clinic 

Aortic arch and its anomalies 

A right-sided arch of aorta occasionally occurs and 
may be asymptomatic. It can be associated with 
dextrocardia (right-sided heart) and, in some instances, 
with complete situs inversus (left-to-right inversion of 
the body's organs). It can also be associated with 
abnormal branching of the great vessels. 


In the clinic 

Thoracic aorta 

Diffuse atherosclerosis of the thoracic aorta may occur 
in patients with vascular disease, but this rarely 
produces symptoms. There are, however, two clinical 
situations in which aortic pathology can produce 
life-threatening situations. 

Trauma 

The aorta has three fixed points of attachment: 

■ the aortic valve, 

■ the ligamentum arteriosum, and 

■ the point of passing behind the median arcuate 
ligament of the diaphragm to enter the abdomen. 

The rest of the aorta is relatively free from 
attachment to other structures of the mediastinum. 

A serious deceleration injury (e.g., in a road traffic 
accident) is most likely to cause aortic trauma at these 
fixed points. 

Aortic Dissection 

In certain conditions, such as in severe arteriovascular 
disease, the wall of the aorta can split longitudinally, 
creating a false channel, which may or may not rejoin 
into the true lumen distally. This aortic dissection occurs 
between the intima and media anywhere along its 
length. If it occurs in the ascending aorta or arch of the 
aorta, blood flow in the coronary and cerebral arteries 
may be disrupted, resulting in myocardial infarction or 
stroke. In the abdomen the visceral vessels may be 
disrupted, producing ischemia to the gut or kidneys. 


In the clinic 

Abnormal origin of great vessels 

Great vessels occasionally have an abnormal origin, 
including: 

■ a common origin of the brachiocephalic trunk and 
the left common carotid artery, 

■ the left vertebral artery originating from the aortic 
arch, and 

■ the right subclavian artery originating from the 
distal portion of the aortic arch and passing 
behind the esophagus to supply the right arm—as 
a result, the great vessels form a vascular ring 
around the trachea and the esophagus, which can 
potentially produce difficulty swallowing. 


217 



Thorax 


Trachea and esophagus 

The trachea is a midline structure that is palpable in the 
jugular notch as it enters the superior mediastinum. 
Posterior to it is the esophagus, which is immediately ante¬ 
rior to the vertebral column (Fig. 3.85, and see Figs. 3.79 
and 3.80). Significant mobility exists in the vertical posi¬ 
tioning of these structures as they pass through the 
superior mediastinum. Swallowing and breathing cause 
positional shifts, as may disease and the use of specialized 
instrumentation. 

As the trachea and esophagus pass through the superior 
mediastinum, they are crossed laterally by the azygos vein 
on the right side and the arch of the aorta on the left side. 


The trachea divides into the right and left main bronchi 
at, or just inferior to, the transverse plane between the 
sternal angle and vertebral levelTIV/V (Fig. 3.86), whereas 
the esophagus continues into the posterior mediastinum. 

Nerves of the superior mediastinum 

Vagus nerves 

The vagus nerves [X] pass through the superior and 
posterior divisions of the mediastinum on their way to 
the abdominal cavity. As they pass through the thorax, 
they provide parasympathetic innervation to the thoracic 
viscera and carry visceral afferents from the thoracic 
viscera. 


Thymus 


Superior vena cava 


Manubrium of sternum 



Right phrenic 
nerve 


Arch of 
azygos vein 


Right vagus 
nerve 


Arch of aorta 


Left phrenic 
nerve 

Left vagus 
nerve 


Arch of 
azygos vein 


Trachea 


Thoracic duct 


Esophagus 


A 


Left recurrent 
laryngeal nerve 



Superior vena cava 


Arch of aorta 


Trachea 


Esophagus 


Fig. 3.85 Cross section through the superior mediastinum at the level of vertebra TIV. A. Diagram. B. Axial computed tomography image. 



218 


Fig. 3.86 Trachea in the superior mediastinum. 




































Regional anatomy • Mediastinum 


3 


Visceral afferents in the vagus nerves relay information 
to the central nervous system about normal physiological 
processes and reflex activities. They do not transmit pain 
sensation. 

Right vagus nerve 

The right vagus nerve enters the superior mediastinum 
and lies between the right brachiocephalic vein and the 


brachiocephalic trunk. It descends in a posterior direction 
toward the trachea (Fig. 3.87), crosses the lateral surface 
of the trachea, and passes posteriorly to the root of the 
right lung to reach the esophagus. Just before the esopha¬ 
gus, it is crossed by the arch of the azygos vein. 

As the right vagus nerve passes through the superior 
mediastinum, it gives branches to the esophagus, cardiac 
plexus, and pulmonary plexus. 



Esophagus 


Esophagus 
Esophageal plexus 


Trachea 

Right vagus nerve 


Azygos vein 
Bronchus 


Brachiocephalic trunk 
Right brachiocephalic vein 


Left brachiocephalic vein 
Superior vena cava 


Right phrenic nerve 


Diaphragm 


Fig. 3.87 Right vagus nerve passing through the superior mediastinum. 


219 




















Thorax 


Left vagus nerve 

The left vagus nerve enters the superior mediastinum 
posterior to the left brachiocephalic vein and between the 
left common carotid and left subclavian arteries (Fig. 3.88). 
As it passes into the superior mediastinum, it lies just deep 
to the mediastinal part of the parietal pleura and crosses 
the left side of the arch of the aorta. It continues to descend 
in a posterior direction and passes posterior to the root of 
the left lung to reach the esophagus in the posterior 
mediastinum. 


As the left vagus nerve passes through the superior 
mediastinum, it gives branches to the esophagus, the 
cardiac plexus, and the pulmonary plexus. 

The left vagus nerve also gives rise to the left recurrent 
laryngeal nerve, which arises from it at the inferior 
margin of the arch of the aorta just lateral to the ligamen- 
tum arteriosum. The left recurrent laryngeal nerve passes 
inferior to the arch of the aorta before ascending on its 
medial surface. Entering a groove between the trachea and 
esophagus, the left recurrent laryngeal nerve continues 



Pericardial sac 


Esophagus 


Thoracic aorta 


Diaphragm 


Left phrenic nerve 
Ligamentum arteriosum 


Left subclavian artery 

Left vagus nerve 

Left recurrent laryngeal nerve 

Left pulmonary artery 


Bronchus 


Rib I 

Left common carotid artery 
Brachiocephalic trunk 
Left brachiocephalic vein 


220 


Fig. 3.88 Left vagus nerve passing through the superior mediastinum. 

















Regional anatomy • Mediastinum 


3 


superiorly to enter the neck and terminate in the larynx 
(Fig. 3.89). 

Phrenic nerves 

The phrenic nerves arise in the cervical region mainly from 
the fourth, but also from the third and fifth, cervical spinal 
cord segments. 

The phrenic nerves descend through the thorax to 
supply motor and sensory innervation to the diaphragm 
and its associated membranes. As they pass through the 
thorax, they provide innervation through somatic afferent 
fibers to the mediastinal pleura, fibrous pericardium, and 
parietal layer of serous pericardium. 

Right phrenic nerve 

The right phrenic nerve enters the superior mediasti¬ 
num lateral to the right vagus nerve and lateral and slightly 



Fig. 3.89 Left recurrent laryngeal nerve passing through the 
superior mediastinum. 


posterior to the beginning of the right brachiocephalic vein 
(see Fig. 3.87). It continues inferiorly along the right side 
of this vein and the right side of the superior vena cava. 

On entering the middle mediastinum, the right phrenic 
nerve descends along the right side of the pericardial sac, 
within the fibrous pericardium, anterior to the root of the 
right lung. The pericardiacophrenic vessels accompany it 
through most of its course in the thorax (see Fig. 3.54). It 
leaves the thorax by passing through the diaphragm with 
the inferior vena cava. 

Left phrenic nerve 

The left phrenic nerve enters the superior mediastinum 
in a position similar to the path taken by the right phrenic 
nerve. It lies lateral to the left vagus nerve and lateral and 
slightly posterior to the beginning of the left brachioce¬ 
phalic vein (see Fig. 3.83), and continues to descend across 
the left lateral surface of the arch of the aorta, passing 
superficially to the left vagus nerve and the left superior 
intercostal vein. 

On entering the middle mediastinum, the left phrenic 
nerve follows the left side of the pericardial sac, within the 
fibrous pericardium, anterior to the root of the left lung, 
and is accompanied by the pericardiacophrenic vessels (see 
Fig. 3.54). It leaves the thorax by piercing the diaphragm 
near the apex of the heart. 


In the clinic 

The vagus nerves, recurrent laryngeal nerves, 
and hoarseness 

The left recurrent laryngeal nerve is a branch of the left 
vagus nerve. It passes between the pulmonary artery 
and the aorta, a region known clinically as the 
aortopulmonary window, and may be compressed in 
any patient with a pathological mass in this region. 

This compression results in vocal cord paralysis and 
hoarseness of the voice. Lymph node enlargement, 
often associated with the spread of lung cancer, is a 
common condition that may produce compression. 

Chest radiography is therefore usually carried out for all 
patients whose symptoms include a hoarse voice. 

More superiorly, in the root of the neck, the right 
vagus nerve gives off the right recurrent laryngeal 
nerve, which "hooks" around the right subclavian artery 
as it passes over the cervical pleura. If a patient has a 
hoarse voice and a right vocal cord palsy is 
demonstrated at laryngoscopy, chest radiography with 
an apical lordotic view should be obtained to assess for 
cancer in the right lung apex (Pancoast's tumor). 

221 




















Thorax 


Thoracic duct in the superior mediastinum 

The thoracic duct, which is the major lymphatic vessel in 
the body, passes through the posterior portion of the supe¬ 
rior mediastinum (see Figs. 3.80 and 3.85). It: 

■ enters the superior mediastinum inferiorly, slightly to 
the left of the midline, having moved to this position just 
before leaving the posterior mediastinum opposite ver¬ 
tebral level TIV/V; and 

■ continues through the superior mediastinum, posterior 
to the arch of the aorta, and the initial portion of the 
left subclavian artery, between the esophagus and the 
left mediastinal part of the parietal pleura. 

Posterior mediastinum 

The posterior mediastinum is posterior to the pericar¬ 
dial sac and diaphragm and anterior to the bodies of the 
mid and lower thoracic vertebrae (see Fig. 3.52). 

■ Its superior boundary is a transverse plane passing from 
the sternal angle to the intervertebral disc between ver¬ 
tebrae TIV and TV. 

■ Its inferior boundary is the diaphragm. 

■ Laterally, it is bordered by the mediastinal part of pari¬ 
etal pleura on either side. 

■ Superiorly, it is continuous with the superior 
mediastinum. 


The esophagus has a slight anterior-to-posterior curva¬ 
ture that parallels the thoracic portion of the vertebral 
column, and is secured superiorly by its attachment to 
the pharynx and inferiorly by its attachment to the 
diaphragm. 

Relationships to important structures in 
the posterior mediastinum 

In the posterior mediastinum, the esophagus is related to a 
number of important structures. The right side is covered 
by the mediastinal part of the parietal pleura. 

Posterior to the esophagus, the thoracic duct is on the 
right side inferiorly, but crosses to the left more superiorly. 
Also on the left side of the esophagus is the thoracic aorta. 

Anterior to the esophagus, below the level of the tra¬ 
cheal bifurcation, are the right pulmonary artery and the 
left main bronchus. The esophagus then passes immedi¬ 
ately posteriorly to the left atrium, separated from it only 
by pericardium. Inferior to the left atrium, the esophagus 
is related to the diaphragm. 

Structures other than the thoracic duct posterior to the 
esophagus include portions of the hemiazygos veins, the 
right posterior intercostal vessels, and, near the diaphragm, 
the thoracic aorta. 

The esophagus is a flexible, muscular tube that can be 
compressed or narrowed by surrounding structures at four 
locations (Fig. 3.91): 


Major structures in the posterior mediastinum 
include the: 

■ esophagus and its associated nerve plexus, 

■ thoracic aorta and its branches, 

■ azygos system of veins, 

■ thoracic duct and associated lymph nodes, 

■ sympathetic trunks, and 

■ thoracic splanchnic nerves. 

Esophagus 

The esophagus is a muscular tube passing between the 
pharynx in the neck and the stomach in the abdomen. It 
begins at the inferior border of the cricoid cartilage, oppo¬ 
site vertebra CVI, and ends at the cardiac opening of the 
stomach, opposite vertebra TXI. 

The esophagus descends on the anterior aspect of the 
bodies of the vertebrae, generally in a midline position as 
it moves through the thorax (Fig. 3.90). As it approaches 
the diaphragm, it moves anteriorly and to the left, crossing 
from the right side of the thoracic aorta to eventually 
assume a position anterior to it. It then passes through the 
esophageal hiatus, an opening in the muscular part of the 
222 diaphragm, at vertebral level TX. 


■ the junction of the esophagus with the pharynx in 
the neck; 

■ in the superior mediastinum where the esophagus is 
crossed by the arch of the aorta; 

■ in the posterior mediastinum where the esophagus is 
compressed by the left main bronchus; 

■ in the posterior mediastinum at the esophageal hiatus 
in the diaphragm. 

These constrictions have important clinical conse¬ 
quences. For example, a swallowed object is most likely to 
lodge at a constricted area. An ingested corrosive sub¬ 
stance would move more slowly through a narrowed 
region, causing more damage at this site than elsewhere 
along the esophagus. Also, constrictions present problems 
during the passage of instruments. 

Arterial supply and venous 
and lymphatic drainage 

The arterial supply and venous drainage of the esopha¬ 
gus in the posterior mediastinum involve many vessels. 
Esophageal arteries arise from the thoracic aorta, bron¬ 
chial arteries, and ascending branches of the left gastric 
artery in the abdomen. 


Regional anatomy • Mediastinum 


3 


Right 



Left common carotid artery 
Left subclavian artery 


Diaphragm 


Arch of aorta 

Left main bronchus 


Esophagus 


Thoracic aorta 


Brachiocephalic trunk 


main bronchus 


Fig. 3.90 Esophagus. 


Venous drainage involves small vessels returning to the 
azygos vein, hemiazygos vein, and esophageal branches to 
the left gastric vein in the abdomen. 

Lymphatic drainage of the esophagus in the posterior 
mediastinum returns to posterior mediastinal and left 
gastric nodes. 

Innervation 

Innervation of the esophagus, in general, is complex. 
Esophageal branches arise from the vagus nerves and sym¬ 
pathetic trunks. 

Striated muscle fibers in the superior portion of the 
esophagus originate from the branchial arches and are 
innervated by branchial efferents from the vagus nerves. 


Smooth muscle fibers are innervated by components of 
the parasympathetic part of the autonomic division of the 
peripheral nervous system, visceral efferents from the 
vagus nerves. These are preganglionic fibers that synapse 
in the myenteric and submucosal plexuses of the enteric 
nervous system in the esophageal wall. 

Sensory innervation of the esophagus involves visceral 
afferent fibers originating in the vagus nerves, sympathetic 
trunks, and splanchnic nerves. 

The visceral afferents from the vagus nerves are 
involved in relaying information back to the central 
nervous system about normal physiological processes and 
reflex activities. They are not involved in the relay of pain 
recognition. 


223 
























Thorax 




Pharynx 


Esophagus 


Trachea 


Where esophagus is 
crossed by arch of 
aorta 

Where esophagus 
is compressed by 
left main bronchus 


Position of 
esophagus 
posterior to 
left atrium 


Diaphragm 


At the esophageal 
hiatus 


Junction of esophagus 
with pharynx 


Fig. 3.91 Sites of normal esophageal constrictions. 


The visceral afferents that pass through the sympa¬ 
thetic trunks and the splanchnic nerves are the primary 
participants in detection of esophageal pain and transmis¬ 
sion of this information to various levels of the central 
nervous system. 

Esophageal plexus 

After passing posteriorly to the root of the lungs, the right 
and left vagus nerves approach the esophagus. As they 
reach the esophagus, each nerve divides into several 
branches that spread over this structure, forming the 
esophageal plexus (Fig. 3.92). There is some mixing of 
fibers from the two vagus nerves as the plexus continues 
inferiorly on the esophagus toward the diaphragm. Just 
above the diaphragm, fibers of the plexus converge to form 
two trunks: 

■ the anterior vagal trunk on the anterior surface of 
the esophagus, mainly from fibers originally in the left 
vagus nerve; 

■ the posterior vagal trunk on the posterior surface of 
the esophagus, mainly from fibers originally in the right 

224 vagus nerve. 



Posterior vagal 
trunk 


Esophageal 

plexus 


Left vagus nerve 


Right vagus 
nerve 


Anterior vagal trunk 


Stomach 


Esophagus 


Fig. 3.92 Esophageal plexus. 


The vagal trunks continue on the surface of the esopha¬ 
gus as it passes through the diaphragm into the abdomen. 


In the clinic 
Esophageal cancer 

When patients present with esophageal cancer, it is 
important to note which portion of the esophagus 
contains the tumor because tumor location determines 
the sites to which the disease will spread. 

Esophageal cancer spreads quickly to lymphatics, 
draining to lymph nodes in the neck and around the 
celiac artery. Endoscopy or barium swallow is used to 
assess the site. CT and MRI may be necessary to stage 
the disease. 

Once the extent of the disease has been assessed, 
treatment can be planned. 
























Regional anatomy • Mediastinum 


3 


In the clinic 
Esophageal rupture 

The first case of esophageal rupture was described by 
Herman Boerhaave in 1724. This case was fatal, but 
early diagnosis has increased the survival rate up to 
65%. If the disease is left untreated, mortality is 100%. 

Typically, the rupture occurs in the lower third of 
the esophagus with a sudden rise in intraluminal 
esophageal pressure produced by vomiting secondary 
to an uncoordination and failure of the cricopharyngeus 
muscle to relax. Because the tears typically occur on the 
left, they are often associated with a large left pleural 
effusion that contains the gastric contents. In some 
patients, subcutaneous emphysema may be 
demonstrated. 

Treatment is optimal with urgent surgical repair. 


Thoracic aorta 

The thoracic portion of the descending aorta (thoracic 
aorta) begins at the lower edge of vertebra TIV, where it is 
continuous with the arch of the aorta. It ends anterior to 
the lower edge of vertebra TXII, where it passes through 
the aortic hiatus posterior to the diaphragm. Situated 
to the left of the vertebral column superiorly, it approaches 
the midline inferiorly, lying directly anterior to the lower 
thoracic vertebral bodies (Fig. 3.93). Throughout its 
course, it gives off a number of branches, which are sum¬ 
marized in Table 3.3. 


Trachea Left subclavian artery 



Supreme 
intercostal 


Right 
bronchial 
artery 


Superior left 
bronchial 
artery 


Esophagus 


Arch of aorta 


Posterior 

intercostal 

arteries 


Esophageal 

branches 


Mediastinal 

branches 


Esophagus 


Fig. 3.93 Thoracic aorta and branches. 


Table 3.3 Branches of the thoracic aorta 


Branches 

Pericardial branches 
Bronchial branches 

Esophageal branches 


Mediastinal branches 

Posterior intercostal arteries 


Superior phrenic arteries 
Subcostal artery 


Origin and course 

A few small vessels to the posterior surface of the pericardial sac 

Vary in number, size, and origin—usually, two left bronchial arteries from the thoracic aorta and one 
right bronchial artery from the third posterior intercostal artery or the superior left bronchial artery 

Four or five vessels from the anterior aspect of the thoracic aorta, which form a continuous 
anastomotic chain—anastomotic connections include esophageal branches of the inferior thyroid 
artery superiorly, and esophageal branches of the left inferior phrenic and the left gastric arteries 
inferiorly 

Several small branches supplying lymph nodes, vessels, nerves, and areolar tissue in the posterior 
mediastinum 

Usually, nine pairs of vessels branching from the posterior surface of the thoracic aorta—usually supply 
lower nine intercostal spaces (first two spaces are supplied by the supreme intercostal artery—a 
branch of the costocervical trunk) 

Small vessels from the lower part of the thoracic aorta supplying the posterior part of the superior 
surface of the diaphragm—they anastomose with the musculophrenic and pericardiacophrenic arteries 

The lowest pair of branches from the thoracic aorta located inferior to rib XII 


225 



























Thorax 


Azygos system of veins 

The azygos system of veins consists of a series of longitu¬ 
dinal vessels on each side of the body that drain blood from 
the body wall and move it superiorly to empty into the 
superior vena cava. Blood from some of the thoracic viscera 


may also enter the system, and there are anastomotic con¬ 
nections with abdominal veins. 

The longitudinal vessels may or may not be continuous 
and are connected to each other from side to side at various 
points throughout their course (Fig. 3.94). 



Posterior intercostal vein 


Hemiazygos vein 


Opening of azygos vein 
into superior vena cava 


Right subcostal vein 


Right ascending lumbar vein 


Right superior intercostal vein 


Left superior intercostal vein 


Ascending lumbar vein 


Inferior vena cava 


Azygos vein 


Accessory hemiazygos 
vein 


Fig. 3.94 Azygos system of veins. 


226 























Regional anatomy • Mediastinum 


3 


The azygos system of veins serves as an important anas¬ 
tomotic pathway capable of returning venous blood from 
the lower part of the body to the heart if the inferior vena 
cava is blocked. 

The major veins in the system are: 

■ the azygos vein, on the right; and 

■ the hemiazygos vein and the accessory hemiazygos vein, 
on the left. 

There is significant variation in the origin, course, tribu¬ 
taries, anastomoses, and termination of these vessels. 

Azygos vein 

The azygos vein arises opposite vertebra LI or LII at the 
junction between the right ascending lumbar vein and 
the right subcostal vein (Fig. 3.94). It may also arise as 
a direct branch of the inferior vena cava, which is joined 
by a common trunk from the junction of the right ascend¬ 
ing lumbar vein and the right subcostal vein. 

The azygos vein enters the thorax through the aortic 
hiatus of the diaphragm, or it enters through or posterior 
to the right crus of the diaphragm. It ascends through the 
posterior mediastinum, usually to the right of the thoracic 
duct. At approximately vertebral level TTV, it arches anteri¬ 
orly, over the root of the right lung, to join the superior 
vena cava before the superior vena cava enters the pericar¬ 
dial sac. 

Tributaries of the azygos vein include: 

■ the right superior intercostal vein (a single vessel 
formed by the junction of the second, third, and fourth 
intercostal veins), 

■ fifth to eleventh right posterior intercostal veins, 

■ the hemiazygos vein, 

■ the accessory hemiazygos vein, 

■ esophageal veins, 

■ mediastinal veins, 

■ pericardial veins, and 

■ right bronchial veins. 

Hemiazygos vein 

The hemiazygos vein (inferior hemiazygos vein) 

usually arises at the junction between the left ascending 


lumbar vein and the left subcostal vein (Fig. 3.94). It 
may also arise from either of these veins alone and often 
has a connection to the left renal vein. 

The hemiazygos vein usually enters the thorax through 
the left crus of the diaphragm, but may enter through the 
aortic hiatus. It ascends through the posterior mediasti¬ 
num, on the left side, to approximately vertebral level TIX. 
At this point, it crosses the vertebral column, posterior to 
the thoracic aorta, esophagus, and thoracic duct, to enter 
the azygos vein. 

Tributaries joining the hemiazygos vein include: 

■ the lowest four or five left posterior intercostal veins, 

■ esophageal veins, and 

■ mediastinal veins. 

Accessory hemiazygos vein 

The accessory hemiazygos vein (superior hemiazygos 
vein) descends on the left side from the superior portion of 
the posterior mediastinum to approximately vertebral level 
TVIII (Fig. 3.94). At this point, it crosses the vertebral 
column to join the azygos vein, or ends in the hemiazygos 
vein, or has a connection to both veins. Usually, it also has 
a connection superiorly to the left superior intercostal 
vein. 

Vessels that drain into the accessory hemiazygos vein 
include: 

■ the fourth to eighth left posterior intercostal veins, and 

■ sometimes, the left bronchial veins. 

Thoracic duct in the posterior mediastinum 

The thoracic duct is the principal channel through which 
lymph from most of the body is returned to the venous 
system. It begins as a confluence of lymph trunks in the 
abdomen, sometimes forming a saccular dilation referred 
to as the cisterna chyli (chyle cistern), which drains 
the abdominal viscera and walls, pelvis, perineum, and 
lower limbs. 

The thoracic duct extends from vertebra LII to the root 
of the neck. 


227 



Thorax 


Entering the thorax, posterior to the aorta, through the 
aortic hiatus of the diaphragm, the thoracic duct ascends 
through the posterior mediastinum to the right of midline 
between the thoracic aorta on the left and the azygos vein 
on the right (Fig. 3.95). It lies posterior to the diaphragm 
and the esophagus and anterior to the bodies of the 
vertebrae. 

At vertebral level TV, the thoracic duct moves to the left 
of midline and enters the superior mediastinum. It contin¬ 
ues through the superior mediastinum and into the neck. 

After being joined, in most cases, by the left jugular 
trunk, which drains the left side of the head and neck, and 


the left subclavian trunk, which drains the left upper 
limb, the thoracic duct empties into the junction of the left 
subclavian and left internal jugular veins. 

The thoracic duct usually receives the contents from: 

■ the confluence of lymph trunks in the abdomen, 

■ descending thoracic lymph trunks draining the lower 
six or seven intercostal spaces on both sides, 

■ upper intercostal lymph trunks draining the upper left 
five or six intercostal spaces, 

■ ducts from posterior mediastinal nodes, and 

■ ducts from posterior diaphragmatic nodes. 



Cisterna chyli 


Right common carotid artery 


Superior vena cava 


Azygos vein 


Thoracic duct 


Hemiazygos vein 


Thoracic duct 


Left brachiocephalic vein 


Accessory 
hemiazygos vein 


Esophagus 


228 


Fig. J.95 Thoracic duct. 

























Regional anatomy • Mediastinum 


3 


Sympathetic trunks 

The sympathetic trunks are an important component 
of the sympathetic part of the autonomic division of the 
peripheral nervous system and are usually considered a 
component of the posterior mediastinum as they pass 
through the thorax. 

This portion of the sympathetic trunks consists of two 
parallel cords punctuated by 11 or 12 ganglia (Fig. 3.96). 
The ganglia are connected to adjacent thoracic spinal 
nerves by white and gray rami communicantes and are 
numbered according to the thoracic spinal nerve with 
which they are associated. 

In the superior portion of the posterior mediastinum, 
the trunks are anterior to the neck of the ribs. Interiorly, 


they become more medial in position until they lie on the 
lateral aspect of the vertebral bodies. The sympathetic 
trunks leave the thorax by passing posterior to the dia¬ 
phragm under the medial arcuate ligament or through the 
crura of the diaphragm. Throughout their course the 
trunks are covered by parietal pleura. 

Branches from the ganglia 

Two types of medial branches are given off by the ganglia: 

■ The first type includes branches from the upper five 
ganglia. 

■ The second type includes branches from the lower seven 
ganglia. 



Sympathetic ganglion 


Sympathetic trunk 


Gray and white 
rami communicantes 


Intercostal nerve 
(anterior ramus of 
thoracic spinal nerve) 


Greater splanchnic 
nerve 

Lesser splanchnic 
nerve 

Least splanchnic 
nerve 


Fig. 3.96 Thoracic portion of sympathetic trunks. 


229 























Thorax 


The first type, which includes branches from the upper 
five ganglia, consists mainly of postganglionic sympathetic 
fibers, which supply the various thoracic viscera. These 
branches are relatively small, and also contain visceral 
afferent fibers. 

The second type, which includes branches from the 
lower seven ganglia, consists mainly of preganglionic sym¬ 
pathetic fibers, which supply the various abdominal and 
pelvic viscera. These branches are large, also carry visceral 
afferent fibers, and form the three thoracic splanchnic 
nerves referred to as the greater, lesser, and least splanch¬ 
nic nerves (Fig. 3.96). 

■ The greater splanchnic nerve on each side usually 
arises from the fifth to ninth or tenth thoracic ganglia. 
It descends across the vertebral bodies moving in a 
medial direction, passes into the abdomen through 
the crus of the diaphragm, and ends in the celiac 
ganglion. 

■ The lesser splanchnic nerve usually arises from the 
ninth and tenth, or tenth and eleventh thoracic ganglia. 
It descends across the vertebral bodies moving in a 
medial direction, and passes into the abdomen through 
the crus of the diaphragm to end in the aorticorenal 
ganglion. 


■ The least splanchnic nerve (lowest splanchnic 
nerve) usually arises from the twelfth thoracic gan¬ 
glion. It descends and passes into the abdomen through 
the crus of the diaphragm to end in the renal plexus. 

Anterior mediastinum 

The anterior mediastinum is posterior to the body of the 
sternum and anterior to the pericardial sac (see Fig. 3.52). 

■ Its superior boundary is a transverse plane passing 
from the sternal angle to the intervertebral disc between 
vertebra TIV and TV, separating it from the superior 
mediastinum. 

■ Its inferior boundary is the diaphragm. 

■ Laterally, it is bordered by the mediastinal part of pari¬ 
etal pleura on either side. 

The major structure in the anterior mediastinum is a 
portion of thymus, described previously (see Fig. 3.81). 
Also present are fat, connective tissue, lymph nodes, medi¬ 
astinal branches of the internal thoracic vessels, and ster¬ 
nopericardial ligaments, which pass from the posterior 
surface of the body of the sternum to the fibrous 
pericardium. 


230 


Surface anatomy • Howto Count Ribs 


3 


Surface anatomy 

Thorax surface anatomy 

The ability to visualize how anatomical structures in the 
thorax are related to surface features is fundamental to a 
physical examination. Landmarks on the body’s surface 
can be used to locate deep structures and to assess function 
by auscultation and percussion. 

How to count ribs 

Knowing how to count ribs is important because different 
ribs provide palpable landmarks for the positions of deeper 


structures. To determine the location of specific ribs, 
palpate the jugular notch at the superior extent of the 
manubrium of the sternum. Move down the sternum until 
a ridge is felt. This ridge is the sternal angle, which identi¬ 
fies the articulation between the manubrium of the 
sternum and the body of the sternum. The costal cartilage 
of rib II articulates with the sternum at this location. Iden¬ 
tify rib II. Then continue counting the ribs, moving in a 
downward and lateral direction (Fig. 3.97). 



Rib X 


Rib I 

Manubrium of sternum 
Body of sternum 


Coracoid process 
Sternal angle 


Xiphoid process 


Jugular notch 
Sternoclavicular joint 


Clavicle 


Costal cartilage 


Costal margin 



Rib X 


Rib I 

Manubrium of sternum 

Body of sternum 


Coracoid process 
Sternal angle 


Jugular notch 
Sternoclavicular joint 


Clavicle 


Xiphoid process 


Costal cartilage 


Costal margin 


Fig. 3.97 Anterior view of chest wall with the locations of skeletal structures shown. A. In women. The location of the nipple relative to a 
specific intercostal space varies depending on the size of the breasts, which may not be symmetrical. B. In men. Note the location of the 
nipple in the fourth intercostal space. 


231 







Thorax 


Surface anatomy of the breast in women 

Although breasts vary in size, they are normally positioned 
on the thoracic wall between ribs II and VI and overlie the 
pectoralis major muscles. Each mammary gland extends 
superolaterally around the lower margin of the pectoralis 
major muscle and enters the axilla (Fig. 3.98). This portion 
of the gland is the axillary tail or axillary process. The posi¬ 
tions of the nipple and areola vary relative to the chest wall 
depending on breast size. 


Visualizing structures at the TIV/V 
vertebral level 

The TIV/V vertebral level is a transverse plane that passes 
through the sternal angle on the anterior chest wall and 
the intervertebral disc between TIV and TV vertebrae pos¬ 
teriorly. This plane can easily be located, because the joint 
between the manubrium of the sternum and the body of 
the sternum forms a distinct bony protuberance that can 
be palpated. At the TIV/V level (Fig. 3.99): 



Areola Nipple 



Fig. 3.98 A. Close-up view of nipple and surrounding areola of 
the breast. B. Lateral view of the chest wall of a woman showing 
the axillary process of the breast. 


■ The costal cartilage of rib II articulates with the 
sternum. 

■ The superior mediastinum is separated from the inferior 
mediastinum. 

■ The ascending aorta ends and the arch of the aorta 
begins. 

■ The arch of the aorta ends and the thoracic aorta 
begins. 

■ The trachea bifurcates. 


232 










Surface anatomy • Visualizing Structures at the TIV/V Vertebral Level 


3 



233 



Thorax 


Visualizing structures in the 
superior mediastinum 

A number of structures in the superior mediastinum in 
adults can be visualized based on their positions relative to 
skeletal landmarks that can be palpated through the skin 
(Fig. 3.100). 

■ On each side, the internal jugular and subclavian 
veins join to form the brachiocephalic veins behind 
the sternal ends of the clavicles near the sternoclavicu¬ 
lar joints. 


The left brachiocephalic vein crosses from left to right 
behind the manubrium of the sternum. 

The brachiocephalic veins unite to form the superior 
vena cava behind the lower border of the costal carti¬ 
lage of the right first rib. 

The arch of the aorta begins and ends at the transverse 
plane between the sternal angle anteriorly and vertebral 
level TIV/V posteriorly. The arch may reach as high as 
the midlevel of the manubrium of the sternum. 


Right common carotid artery Trachea Esophagus 



Right internal jugular vein 


Right subclavian artery 


Left common carotid artery 

Left internal jugular vein 
Left subclavian artery 

Left subclavian vein 


Right subclavian vein 


Right 

brachiocephalic vein 


Superior 
vena cava 

Right pulmonary 
artery 


Right main 
bronchus 


Left brachiocephalic 
vein 

Arch of aorta 

Left pulmonary 
artery 

Left main bronchus 


Pulmonary trunk 


Esophagus Ascending aorta Thoracic aorta 


Fig. 3.100 Anterior view of the chest wall of a man showing the locations of different structures in the superior mediastinum as they relate 
to the skeleton. 


234 



Surface anatomy • Visualizing the Margins of the Heart 


3 


Visualizing the margins of the heart 

Surface landmarks can be palpated to visualize the outline 

of the heart (Fig. 3.101). 

■ The upper limit of the heart reaches as high as the 
third costal cartilage on the right side of the sternum 
and the second intercostal space on the left side of the 
sternum. 

■ The right margin of the heart extends from the right 
third costal cartilage to near the right sixth costal 
cartilage. 


■ The left margin of the heart descends laterally from the 
second intercostal space to the apex located near the 
midclavicular line in the fifth intercostal space. 

■ The lower margin of the heart extends from the sternal 
end of the right sixth costal cartilage to the apex in the 
fifth intercostal space near the midclavicular line. 



Sixth costal cartilage 


Fig. 3.101 Anterior view of the chest 


wall of 


Second intercostal space 


Fifth intercostal space 


Midclavicular line 


+ 

a man showing skeletal structures and the surface projection of the heart. 


Third costal cartilage 


235 









Thorax 


Where to listen for heart sounds 

To listen for valve sounds, position the stethoscope down¬ 
stream from the flow of blood through the valves 
(Fig. 3.102). 

■ The tricuspid valve is heard just to the left of the lower 
part of the sternum near the fifth intercostal space. 

■ The mitral valve is heard over the apex of the heart in 
the left fifth intercostal space at the midclavicular line. 

■ The pulmonary valve is heard over the medial end of the 
left second intercostal space. 

■ The aortic valve is heard over the medial end of the right 
second intercostal space. 

Visualizing the pleural cavities and lungs, 
pleural recesses, and lung lobes and fissures 

Palpable surface landmarks can be used to visualize the 
normal outlines of the pleural cavities and the lungs 
and to determine the positions of the pulmonary lobes 
and fissures. 


Superiorly, the parietal pleura projects above the first 
costal cartilage. Anteriorly, the costal pleura approaches 
the midline posterior to the upper portion of the sternum. 
Posterior to the lower portion of the sternum, the left 
parietal pleura does not come as close to the midline as it 
does on the right side. This is because the heart bulges onto 
the left side (Fig. 3.103A). 

Interiorly, the pleura reflects onto the diaphragm above 
the costal margin and courses around the thoracic wall 
following an VIII, X, XII contour (i.e., rib VIII in the mid- 
clavicular line, rib X in the midaxillary line, and vertebra 
TXII posteriorly). 

The lungs do not completely fill the area surrounded 
by the pleural cavities, particularly anteriorly and 
inferiorly. 

■ Costomediastinal recesses occur anteriorly, particularly 
on the left side in relationship to the heart bulge. 

■ Costodiaphragmatic recesses occur inferiorly between 
the lower lung margin and the lower margin of the 
pleural cavity. 


236 



Tricuspid valve 


Mitral valve 


Auscultation position 
for aortic valve 


Aortic valve 


Auscultation position 
for tricuspid valve 


Auscultation position 
for mitral valve 


Auscultation position 
for pulmonary valve 


Pulmonary valve 


Fig. 3.102 Anterior view of the chest wall of a man showing skeletal structures, heart, location of the heart valves, and auscultation points. 














Surface anatomy • Visualizing the Pleural Cavities and Lungs, Pleural Recesses, and Lung Lobes and Fissures 


3 


Superior lobe 

Horizontal fissure 

Middle lobe 

Rib VI 

Inferior lobe - 

Rib VIII 

Rib X 

Parietal pleura 

A 



Superior lobe 


Costomediastinal 

recess 

Inferior lobe 


Costodiaphragmatic 

recess 


Rib V 
Rib VI 


Rib X 


B 



Upper lobe 

Oblique fissure 


Lower lobe 


Parietal pleura 


Fig. 3.103 Views of the chest wall showing the surface projections of the lobes and the fissures of the lungs. A. Anterior view in a woman. 
On the right side, the superior, middle, and inferior lobes are illustrated. On the left side, the superior and inferior lobes are illustrated. 

B. Posterior view in a woman. On both sides, the superior and inferior lobes are illustrated. The middle lobe on the right side is not visible 
in this view. 


237 




























Thorax 


In quiet respiration, the inferior margin of the lungs 
travels around the thoracic wall following a VI, VIII, X 
contour (i.e., rib VI in the midclavicular line, rib VIII in the 
midaxillary line, and vertebra TX posteriorly). 

In the posterior view, the oblique fissure on both sides 
is located in the midline near the spine of vertebra TIV 
(Figs. 3.103B and 3.104A). It moves laterally in a down¬ 
ward direction, crossing the fourth and fifth intercostal 
spaces and reaches rib VI laterally. 


In the anterior view, the horizontal fissure on the right 
side follows the contour of rib IV and its costal cartilage 
and the oblique fissures on both sides follow the contour of 
rib VI and its costal cartilage (Fig. 3.104B). 

Where to listen for lung sounds 

The stethoscope placements for listening for lung sounds 
are shown in Fig. 3.105. 



Fig. 3.104 Views of the chest wall. A. Posterior view in a woman with arms abducted and hands positioned behind her head. On both sides, 
the superior and inferior lobes of the lungs are illustrated. When the scapula is rotated into this position, the medial border of the scapula 
parallels the position of the oblique fissure and can be used as a guide for determining the surface projection of the superior and inferior 
lobes of the lungs. 


238 












Surface anatomy • Where to Listen for Lung Sounds 


3 


B 


Superior lobe 
TIV spine 
Rib V 
Rib VI 
Middle lobe 

Inferior lobe 
Rib VIII 

Rib X 
Midaxillary line 



Horizontal fissure 
Oblique fissure 


Parietal pleura 

Costodiaphragmatic 

recess 


Fig. 3.104, cont’d B. Lateral view in a man with his right arm abducted. The superior, middle, and inferior lobes of the right lung are 
illustrated. The oblique fissure begins posteriorly at the level of the spine of vertebra TIV, passes inferiorly crossing rib IV, the fourth 
intercostal space, and rib V. It crosses the fifth intercostal space at the midaxillary line and continues anteriorly along the contour of rib VI. 
The horizontal fissure crosses rib V in the midaxillary space and continues anteriorly, crossing the fourth intercostal space and following the 
contour of rib IV and its costal cartilage to the sternum. 


239 


















Thorax 




( 4 J 


Middle lobe of right lung 


Inferior lobe of right lung 


Apex of left lung 


Superior lobe of left lung 


Inferior lobe of left lung 

B 

Fig. 3.105 Views of the chest wall of a man with stethoscope placements for listening to the lobes of the lungs. A. Anterior views. 
B. Posterior views. 


240 





















Clinical cases • Case 1 


3 


Clinical cases 


Case 1 


CERVICAL RIB 

A young man has black areas of skin on the tips of his 
fingers of his left hand. A clinical diagnosis of platelet 
emboli was made and a source of the emboli sought. 

Emboli can arise from many sources. They are clots and 
plugs of tissue, usually platelets, that are carried from a 
source to eventually reside in small vessels which they 
may occlude. Arterial emboli may arise in the heart or in 
the arteries that supply the region affected. In cases of 
infected emboli, bacteria grow on the valve and are 
showered off into the peripheral circulation. 

A neck radiograph and coronal CT image of the neck 
demonstrates a cervical rib (Fig. 3.106). 

Cervical ribs may produce three distinct disease entities: 

■ Arterial compression and embolization—the cervical 
rib (or band) on the undersurface of the distal portion 
of the subclavian artery reduces the diameter of the 
vessel and allows eddy currents to form. Platelets 
aggregate and atheroma may develop in this region. 
This debris can be dislodged and flow distally within 
the upper limb vessels to block off blood flow to the 
fingers and the hand, a condition called distal 
embolization. 

■ Tension on the T1 nerve—the T1 nerve, which normally 
passes over rib I, is also elevated by the presence of a 
cervical rib; thus the patient may experience a sensory 
disturbance over the medial aspect of the forearm, and 
develop wasting of the intrinsic muscles of the hand. 

■ Compression of the subclavian vein—this may induce 
axillary vein thrombosis. 

A Doppler ultrasound scan revealed marked stenosis of 
the subclavian artery at the outer border of the rib with 
abnormal flow distal to the narrowing. Within this region 
of abnormal flow there was evidence of thrombus 
adherent to the vessel wall. 



Fig. 3.106 Cervical ribs. A. Neck radiograph demonstrating 
bilateral cervical ribs. B. Coronal computed tomography 
image showing cervical ribs. 


This patient underwent surgical excision of the cervical 
rib and had no further symptoms. 


241 








Thorax 



Case 2 

LUNG CANCER 

A 52-year-old man presented with headaches and 
shortness of breath. He also complained of coughing 
up small volumes of blood. Clinical examination 
revealed multiple dilated veins around the neck. 

A chest radiograph demonstrated an elevated 
diaphragm on the right and a tumor mass, which was 
believed to be a primary bronchogenic carcinoma. 

By observing the clinical findings and applying 
anatomical knowledge, the site of the tumor can be 
inferred. 


The multiple dilated veins around the neck are indicative 
of venous obstruction. The veins are dilated on both 
sides of the neck, implying that the obstruction must be 
within a common vessel, the superior vena cava. Anterior 
to the superior vena cava in the right side of the chest is 
the phrenic nerve, which supplies the diaphragm. 
Because the diaphragm is elevated, suggesting paralysis, 
it is clear that the phrenic nerve has been involved with 
the tumor. 


Case 3 

CHEST WOUND 

A 35-year-old man was shot during an armed robbery. 
The bullet entry wound was in the right fourth 
intercostal space, above the nipple. A chest 
radiograph obtained on admission to the emergency 
room demonstrated complete collapse of the lung. 

A further chest radiograph performed 20 minutes 
later demonstrated an air/fluid level in the pleural 
cavity (Fig. 3.107). 



Fig. 3.107 Chest radiograph demonstrating an air/fluid level 
in the pleural cavity. 


Three common pathological processes may occur in the 
pleural cavity. 

■ If air is introduced into the pleural cavity, a 
pneumothorax develops and the lung collapses 
because of its own elastic recoil. The pleural space fills 
with air, which may further compress the lung. Most 
patients with a collapsed lung are unlikely to have 
respiratory impairment. Under certain conditions, air 
may enter the pleural cavity at such a rate that it shifts 
and pushes the mediastinum to the opposite side of 
the chest. This is called tension pneumothorax and 
is potentially lethal, requiring urgent treatment by 
insertion of an intercostal tube to remove the air. The 
commonest causes of pneumothorax are rib fractures 
and positive pressure ventilation lung damage. 

■ The pleural cavity may fill with fluid (a pleural effusion) 
and this can be associated with many diseases 

(e.g., lung infection, cancer, abdominal sepsis). It is 
important to aspirate fluid from these patients to 
relieve any respiratory impairment and to carry out 
laboratory tests on the fluid to determine its nature. 

■ Severe chest trauma can lead to development of 
hemopneumothorax. A tube must be inserted to 
remove the blood and air that has entered the pleural 
space and prevent respiratory impairment. 

This man needs treatment to drain either the air or fluid 
or both. 

The pleural space can be accessed by passing a needle 
between the ribs into the pleural cavity. In a normal 
healthy adult, the pleural space is virtually nonexistent; 
therefore, any attempt to introduce a needle into this 

(continues) 


242 




Clinical cases • Cose 4 


3 


Case 3 (continued) 

space is unlikely to succeed and the procedure may 
damage the underlying lung. 

Before any form of chest tube is inserted, the rib must be 
well anesthetized by infiltration because its periosteum 
is extremely sensitive. The intercostal drain should pass 
directly on top of the rib. Insertion adjacent to the lower 
part of the rib may damage the artery, vein, and nerve, 
which lie within the neurovascular bundle. 

Appropriate sites for insertion of a chest drain are either 
in the fourth or fifth intercostal space between the 


anterior axillary and midaxillary anatomical lines. 

This position is determined by palpating the sternal 
angle, which is the point of articulation of rib II. Counting 
interiorly will determine the rib number and simple 
observation will determine the positions of the anterior 
axillary and midaxillary lines. Insertion of any tube or 
needle below the fifth interspace runs an appreciable risk 
of crossing the pleural recesses and placing the needle or 
the drain into either the liver or the spleen, depending 
upon which side the needle is inserted. 


Case 4 

MYOCARDIAL INFARCTION 

A 65-year-old man was admitted to the emergency 
room with severe central chest pain that radiated to 
the neck and predominantly to the left arm. He was 
overweight and a known heavy smoker. 

On examination he appeared gray and sweaty. His 
blood pressure was 74/40 mm Hg (normal range 
120/80 mm Hg). An electrocardiogram (ECG) was 
performed and demonstrated anterior myocardial 
infarction. An urgent echocardiograph demonstrated 
poor left ventricular function. The cardiac angiogram 


revealed an occluded vessel (Fig. 3.108A,B). Another 
approach to evaluating coronary arteries in patients is to 
perform maximum intensity projection (MIP) CT studies 

(Fig. 3.109A,B). 

This patient underwent an emergency coronary artery 
bypass graft and made an excellent recovery. He has now 
lost weight, stopped smoking, and exercises regularly. 

When cardiac cells die during a myocardial infarction, 
pain fibers (visceral afferents) are stimulated. These 
visceral sensory fibers follow the course of sympathetic 
fibers that innervate the heart and enter the spinal cord 



Fig. 3.108 A. Normal left coronary artery angiogram. B. Left coronary artery angiogram showing decreased flow due to blockages. 


(continues) 


243 





Thorax 



Case 4 (continued) 



Fig. 3.108, cont’d C. Mechanism for perceiving heart pain in 
Tl-4 dermatomes. 


between the Tl and TIV levels. At this level, somatic 
afferent nerves from spinal nerves Tl to T4 also enter the 
spinal cord via the posterior roots. Both types of afferents 
(visceral and somatic) synapse with interneurons, which 
then synapse with second neurons whose fibers pass 
across the cord and then ascend to the somatosensory 
areas of the brain that represent the Tl to T4 levels. The 
brain is unable to distinguish clearly between the visceral 
sensory distribution and the somatic sensory distribution 
and therefore the pain is interpreted as arising from the 
somatic regions rather than the visceral organ (i.e., the 
heart; Fig. 3.108C). 

The patient was breathless because his left ventricular 
function was poor. 

When the left ventricle fails, it produces two effects. 

■ First, the contractile force is reduced. This reduces the 
pressure of the ejected blood and lowers the blood 
pressure. 

■ The left atrium has to work harder to fill the failing left 
ventricle. This extra work increases left atrial pressure, 
which is reflected in an increased pressure in the 
pulmonary veins, and this subsequently creates a 
higher pulmonary venular pressure. This rise in 
pressure will cause fluid to leak from the capillaries 
into the pulmonary interstitium and then into the 
alveoli. Such fluid is called pulmonary edema and it 
markedly restricts gas exchange. This results in 
shortness of breath. 

This man had a blocked left coronary artery, as shown in 

Fig. 3.108B. 

It is important to know which coronary artery is blocked. 

■ The left coronary artery supplies the majority of the 
left side of the heart. The left main stem vessel is 
approximately 2 cm long and divides into the 
circumflex artery, which lies between the atrium and 
the ventricle in the coronary sulcus, and the anterior 
interventricular artery, which is often referred to as the 
left anterior descending artery (LAD). 

■ When the right coronary artery is involved with arterial 
disease and occludes, associated disorders of cardiac 
rhythm often result because the sinu-atrial and the 
atrioventricular nodes derive their blood supplies 
predominantly from the right coronary artery. 

(continues) 


244 










Clinical cases • Case 4 


3 


Case 4 (continued) 

When this patient sought medical care, his myocardial 
function was assessed using ECG, echocardiography, and 
angiography. 

During a patient's initial examination, the physician will 
usually assess myocardial function. 

After obtaining a clinical history and carrying out a 
physical examination, a differential diagnosis for the 
cause of the malfunctioning heart is made. Objective 
assessment of myocardial and valve function is obtained 
in the following ways: 

■ ECG/EKG (electrocardiography) —a series of 
electrical traces taken around the long and short axes 
of the heart that reveal heart rate and rhythm and 
conduction defects. In addition, it demonstrates the 
overall function of the right and left sides of the heart 
and points of dysfunction. Specific changes in the ECG 
relate to the areas of the heart that have been involved 
in a myocardial infarction. For example, a right 
coronary artery occlusion produces infarction in 

the area of myocardium it supplies, which is 
predominantly the inferior aspect; the infarct is 
therefore called an inferior myocardial infarction. 

The ECG changes are demonstrated in the leads that 
visualize the inferior aspect of the myocardium 
(namely, leads II, III, and aVF). 

■ Chest radiography —reveals the size of the heart and 
chamber enlargement. Careful observation of the 
lungs will demonstrate excess fluid (pulmonary 
edema), which builds up when the left ventricle fails 
and can produce marked respiratory compromise and 
death unless promptly treated. 


■ Blood tests —the heart releases enzymes during 
myocardial infarction, namely lactate dehydrogenase 
(IDH), creatine kinase (CK), and aspartate 
transaminase (AST). These plasma enzymes are 
easily measured in the hospital laboratory and used 
to determine the diagnosis at an early stage. Further 
specific enzymes termed isoenzymes can also be 
determined (creatine kinase MB isoenzyme [CKMB]). 
Newer tests include an assessment for troponin (a 
specific component of the myocardium), which is 
released when cardiac cells die during myocardial 
infarction. 

■ Exercise testing —patients are connected to an ECG 
monitor and exercised on a treadmill. Areas of 
ischemia, or poor blood flow, can be demonstrated, 
so localizing the vascular abnormality. 

■ Nuclear medicine —thallium (a radioactive X-ray 
emitter) and its derivatives are potassium analogs. 

They are used to determine areas of coronary ischemia. 
If no areas of myocardial uptake are demonstrated 
when these substances are administered to a patient 
the myocardium is dead. 

■ Coronary angiography —small arterial catheters are 
maneuvered from a femoral artery puncture site 
through the femoral artery and aorta and up to the 
origins of the coronary vessels. X-ray contrast medium 
is then injected to demonstrate the coronary vessels 
and their important branches. If there is any narrowing 
(stenosis), angioplasty may be carried out. In 
angioplasty tiny balloons are passed across the 
narrowed areas and inflated to refashion the vessel 
and so prevent further coronary ischemia and 
myocardial infarction. 



Fig. 3.109 Axial maximum intensity projection (MIP) CT image through the heart. A. Normal anterior interventricular (left anterior 
descending) artery. B. Stenotic (calcified) anterior interventricular (left anterior descending) artery. 


245 





Thorax 



Case 5 

BROKEN PACEMAKER 

An elderly woman was admitted to the emergency 
room with severe cardiac failure. She had a left-sided 
pacemaker box, which had been inserted for a cardiac 
rhythm disorder (fast atrial fibrillation) many years 
previously. An ECG demonstrated fast atrial 
fibrillation. A chest radiograph showed that the wire 
from the pacemaker had broken under the clavicle. 

Anatomical knowledge of this region of the chest 
explains why the wire broke. 

Many patients have cardiac pacemakers. A wire arises 
from the pacemaker, which lies within the subcutaneous 
tissue over the pectoralis major muscle and travels from 
the pacemaker under the skin to pierce the axillary vein 
just beneath the clavicle, lateral to the subclavius muscle. 
The wire then passes through the subclavian vein, the 
brachiocephalic vein, the superior vena cava, and the 
right atrium, and lies on the wall of the right ventricle 
(where it can stimulate the heart to contract) (Fig. 3-110). 
If the wire pierces the axillary vein directly adjacent to the 
subclavius muscle, it is possible that after many years of 
shoulder movement the subclavius muscle stresses and 
breaks the wire, causing the pacemaker to fail. Every 
effort is made to place the insertion point of the wire 
as far laterally as feasible within the first part of the 
axillary vein. 



Fig. 3.110 Chest radiograph of an individual with a pacemaker. 
The pacemaker wires ( 2 ) can be seen traveling through the 
venous system to the heart where one ends in the right 
atrium and the other ends in the right ventricle. 


246 




Clinical cases • Case 7 


3 


Case 6 


COARCTATION OF THE AORTA 

A 20-year-old man visited his family doctor because 
he had a cough. A chest radiograph demonstrated 
translucent notches along the inferior border of ribs 
III to VI (Fig. 3.111 ). He was referred to a cardiologist 
and a diagnosis of coarctation of the aorta was made. 
The rib notching was caused by dilated collateral 
intercostal arteries. 

Coarctation of the aorta is a narrowing of the aorta distal 
to the left subclavian artery. This narrowing can markedly 
reduce blood flow to the lower body. Many of the vessels 
above the narrowing therefore enlarge due to the 
increased pressure so that blood can reach the aorta 
below the level of the narrowing. Commonly, the internal 
thoracic, superior epigastric, and musculophrenic arteries 
enlarge anteriorly. These arteries supply the anterior 
intercostal arteries, which anastomose with the posterior 
intercostal arteries that allow blood to flow retrogradely 
into the aorta. Enlargement of the intertcostal vessels 
results in notching of the ribs. 

The first and second posterior intercostal vessels are 
supplied from the costocervical trunk, which arises from 
the subclavian artery proximal to the coarctation, so do 
not enlarge and do not induce rib notching. 



Fig. 3.111 Chest radiograph demonstrating translucent notches 
along the inferior border of ribs III to VI. 


Case 7 

AORTIC DISSECTION 

A 62-year-old man was admitted to the emergency 
room with severe interscapular pain. His past medical 
history indicated that he was otherwise fit and well; 
however, it was noted he was 6 ' 9 " and had undergone 
previous eye surgery for dislocating lenses. 

On examination the man was pale, clammy, and 
hypotensive. The pulse in his right groin was weak. 

An ECG demonstrated an inferior myocardial 
infarction. Serum blood tests revealed poor kidney 
function and marked acidosis. 

The patient was transferred to the CT scanner and a 
diagnosis of aortic dissection was made. 

Aortic dissection is an uncommon disorder in which a 
small tear occurs within the aortic wall (Fig. 3.11 2). The 
aortic wall contains three layers, an intima, a media, and 
an adventitia. A tear in the intima extends into the media 
and peels it away, forming a channel within the wall of 


the vessel. Usually the blood reenters the main vessel 
wall distal to its point of entry. 

The myocardial infarction 

Aortic dissection may extend retrogradely to involve the 
coronary sinus of the right coronary artery. Unfortunately, 
in this patient's case the right coronary artery became 
occluded as the dissection passed into the origin. In 
normal individuals the right coronary artery supplies the 
anterior inferior aspect of the myocardium, and this is 
evident as an anterior myocardial infarct on an ECG. 

The ischemic left leg 

The two channels within the aorta have extended 
throughout the length of the aorta into the right iliac 
system and to the level of the right femoral artery. 
Although blood flows through these structures it often 

(continues) 


247 





Thorax 



Case 7 (continued) 

causes reduced blood flow. Hence the reduced blood 
flow into the left lower limb renders it ischemic. 

The patient became acidotic. 

All cells in the body produce acid, which is excreted in 
the urine or converted into water with the production of 
carbon dioxide, which is removed with ventilation. 
Unfortunately, when organs become extremely ischemic 
they release significant amounts of hydrogen ions. 
Typically, this occurs when the gut becomes ischemic. 
With the pattern of dissection, (1) the celiac trunk, 
superior mesenteric artery, and inferior mesenteric artery 
can be effectively removed from the circulation or (2) the 
blood flow within these vessels can be significantly 
impeded, rendering the gut ischemic and hence 
accounting for the relatively high hydrogen ion levels. 


Kidney ischemia 

Similarly the dissection can impair blood flow to the 
kidneys, which decreases their ability to function. 

Treatment 

The patient underwent emergency surgery and survived. 
Interestingly, the height of the patient and the previous 
lens surgery would suggest a diagnosis of Marfan 
syndrome, and a series of blood tests and review of the 
family history revealed this was so. 


The true lumen surrounded The false lumen Collapsed intima and media 

by the collapsed intima and media 



The true lumen The false lumen 

B 


Fig. 3.112 A. CT image of aortic dissection. B. Normal aorta (left) and an aortic dissection (right). The line in the right figure indicates 
the plane of the CT scan shown in A. 


248 










Clinical cases • Cose 8 


3 


Case 8 

PNEUMONIA 

A 35-year-old male patient presented to his family 
practitioner because of recent weight loss (14 lb over 
the previous 2 months). He also complained of a 
cough with streaks of blood in the sputum 
(hemoptysis) and left-sided chest pain. Recently, he 
noticed significant sweating, especially at night, 
which necessitated changing his sheets. 

On examination the patient had a low-grade 
temperature and was tachypneic (breathing fast). 
There was reduced expansion of the left side of the 
chest. When the chest was percussed it was noted 
that the anterior aspect of the left chest was dull, 
compared to the resonant percussion note of the 
remainder of the chest. Auscultation (listening with a 
stethoscope) revealed decreased breath sounds, 
which were hoarse in nature (bronchial breathing). 

A diagnosis of chest infection was made. 

Chest infection is a common disease. In most patients the 
infection affects the large airways and bronchi. If the 
infection continues, exudates and transudates are 
produced, filling the alveoli and the secondary pulmonary 
lobules. The diffuse patchy nature of this type of infection 
is termed bronchial pneumonia. 

Given the patient's specific clinical findings, bronchial 
pneumonia was unlikely. 

From the clinical findings it was clear that the patient was 
likely to have a pneumonia confined to a lobe. Because 
there are only two lobes in the left lung, the likely 
diagnosis was a left upper lobe pneumonia. 

A chest radiograph was obtained (Fig. 3.11 3). The 
posteroanterior view of the chest demonstrated an area 
of veil-like opacification throughout the whole of the 
left lung. 

Knowing the position of the oblique fissure, any 
consolidation within the left upper lobe will produce 


this veil-like shadowing. Lateral radiographs are usually 
not necessary but would demonstrate opacification 
anteriorly and superiorly that ends abruptly at the 
oblique fissure. 

Upper lobe pneumonias are unusual because most 
patients develop gravity-dependent infection. Certain 
infections, however, are typical within the middle and 
upper lobes, commonly, tuberculosis (TB) and 
histoplasmosis. 

A review of the patient's history suggested a serious and 
chronic illness and the patient was admitted to hospital. 

After admission a bronchoscopy was carried out and 
sputum was aspirated from the left upper lobe bronchus. 
This was cultured in the laboratory and also viewed 
under the microscope and tuberculous bacilli (TB) were 
identified. 



Fig. 3.113 Chest radiograph showing left upper lobe infection. 


249 



Thorax 



Case 9 

ESOPHAGEAL CANCER 

A 68-year-old man came to his family physician 
complaining of discomfort when swallowing 
(dysphagia). The physician examined the patient and 
noted since his last visit he had lost approximately 
18 lb over 6 months. Routine blood tests revealed 
the patient was anemic and he was referred to the 
gastroenterology unit. A diagnosis of esophageal 
cancer was made and the patient underwent a 
resection, which involved a chest and abdominal 
incision. After 4 years the patient remains well 
though still subject to follow-up. 

The patient underwent a flexible endoscopic examination 
of the esophagus in which a tube is placed through the 
mouth and into the esophagus and a camera is placed 
on the end of the tube. It is also possible to use biopsy 
forceps to obtain small portions of tissue for adequate 
diagnosis. 

The diagnosis of esophageal carcinoma was made 
(squamous cell type) and the patient underwent a 
staging procedure. 

Staging of any malignancy is important because it 
determines the extent of treatment and allows the 
physician to determine the patient's prognosis. In this 
case our patient underwent a CT scan of the chest and 
abdomen, which revealed no significant lymph nodes 
around the lower third esophageal tumor. 

The abdominal scan revealed no evidence of spread to 
the nodes around the celiac trunk and no evidence of 
spread to the liver. 

Bleeding was the cause of the anemia. 

Many tumors of the gastrointestinal system are 
remarkably friable, and with the passage of digested 
material across the tumor, low-grade chronic bleeding 
occurs. Over a period of time the patient is rendered 
anemic, which in the first instance is asymptomatic; 
however, it can be diagnosed on routine blood tests. 


Complex surgery is planned. 

The length of the esophagus is approximately 22 cm. 
Tumor spread can occur through the submucosal route 
and also through locoregional lymph nodes. The lymph 
nodes drain along the arterial supply to the esophagus, 
which is predominantly supplied by the inferior thyroid 
artery, esophageal branches from the thoracic aorta, and 
branches from the left gastric artery. The transthoracic 
esophagectomy procedure involves placing the patient 
supine. A laparotomy is performed to assess for any 
evidence of disease in the abdominal cavity. The stomach 
is mobilized, with preservation of the right gastric and 
right gastro-omental arteries. The short gastric vessels 
and left gastric vessels are divided, and a pyloromyotomy 
is also performed. 

The abdominal wound is then closed and the patient 
is placed in the left lateral position. A right posterolateral 
thoracotomy is performed through the fifth intercostal 
space, and the azygos vein is divided to provide full 
access to the whole length of the esophagus. The 
stomach is delivered through the diaphragmatic hiatus. 
The esophagus is resected and the stomach is 
anastomosed to the cervical esophagus. 

The patient made an uneventful recovery. 

Most esophageal cancers are diagnosed relatively late 
and often have lymph node metastatic spread. A number 
of patients will also have a spread of tumor to the liver. 
The overall prognosis for esophageal cancer is poor, with 
approximately a 25%, 5-year survival rate. 

Diagnosing esophageal cancer in its early stages before 
lymph node spread is ideal and can produce a curative 
procedure. 

Our patient went on to have chemotherapy and enjoys a 
good quality of life 4 years after his operation. 


250 


Clinical cases • Cose 10 


3 


Case 10 

VENOUS ACCESS 

A 45-year-old woman, with a history of breast 
cancer in the left breast, returned to her physician. 
Unfortunately the disease had spread to the axillary 
lymph nodes and bones (bony metastatic disease). A 
surgeon duly resected the primary breast tumor with 
a wide local excision and then performed an axillary 
nodal clearance. The patient was then referred to 
an oncologist for chemotherapy. Chemotherapy 
was delivered through a portacath, which is a 
subcutaneous reservoir from which a small catheter 
passes under the skin into the internal jugular vein. 
The patient duly underwent a portacath insertion 
without complication, completed her course of 
chemotherapy, and is currently doing well 
5 years later. 

The portacath was placed on the patient's right anterior 
chest wall and the line was placed into the right internal 
jugular vein. The left internal jugular vein and 
subcutaneous tissues were not used. The reason for not 
using this site was that the patient had previously 
undergone an axillary dissection on the left, and the 
lymph nodes and lymphatics were removed. Placement 
of a portacath in this region may produce an 
inflammatory response and may even get infected. 
Unfortunately, because there are no lymphatics to drain 
away infected material and to remove bacteria, severe 
sepsis and life-threatening infection may ensue. 

How was it placed? 

The ultrasound shows an axial image across the root of 
the neck on the right demonstrating the right common 


carotid artery and the right internal jugular vein. The 
internal jugular vein is the larger of the two structures 
and generally demonstrates normal respiratory variation, 
compressibility, and a size dependence upon the 
patient's position (when the patient is placed in 
the head-down position, the vein fills and makes 
puncture easy). 

The risks of the procedure 

As with all procedures and operations there is always a 
small risk of complication. These risks are always 
balanced against the potential benefits of the procedure. 
Placing the needle into the internal jugular vein can be 
performed under ultrasound guidance, which reduces 
the risk of puncturing the common carotid artery. 
Furthermore, by puncturing under direct vision it is less 
likely that the operator will hit the lung apex and pierce 
the superior pleural fascia, which may produce a 
pneumothorax. 

The position of the indwelling catheter 

The catheter is placed through the right internal jugular 
vein and into the right brachiocephalic vein. The tip of 
the catheter is then placed more interiorly at the junction 
of the right atrium and the superior vena cava. The 
reason for placing the catheter in such a position relates 
to the agents that are infused. Most chemotherapeutic 
agents are severely cytotoxic (kill cells), and enabling 
good mixing with the blood prevents thrombosis and 
vein wall irritation. 


251 



This page intentionally left blank 


Abdomen 


ADDITIONAL LEARNING RESOURCES 
for Chapter 4, Abdomen, 
on STUDENT CONSULT 

( ): 


■ Image Library—illustrations of abdominal 
anatomy, Chapter 4 

■ Self-Assessment—National Board style multiple- 
choice questions, Chapter 4 

■ Short Questions—these are questions requiring 
short responses, Chapter 4 

■ Interactive Surface Anatomy—interactive surface 
animations, Chapter 4 

■ Medical Clinical Case Studies, Chapter 4 
Aorto-iliac occlusive disease 

Colon cancer 
Intussusception 
Zollinger-Ellison syndrome 
Free Online Anatomy and Embryology 
Self-Study Course 

■ Anatomy modules 10 through 17 

■ Embryology modules 65 and 66 




Conceptual overview 

General description 
Functions 

Houses and protects major viscera 
Breathing 258 

Changes in intraabdominal pressure 
Component parts 259 
Wall 259 

Abdominal cavity 260 
Inferior thoracic aperture 
Diaphragm 
Pelvic inlet 

Relationship to other regions 
Thorax 
Pelvis 
Lower limb 
Key features 

Arrangement of abdominal viscera in the 
adult 

Skin and muscles of the anterior and lateral 
abdominal wall and thoracic intercostal 
nerves 

The groin is a weak area in the anterior abdominal 
wall 

Vertebral level LI 

The gastrointestinal system and its derivatives are 
supplied by three major arteries 
Venous shunts from left to right 
All venous drainage from the gastrointestinal 
system passes through the liver 
Abdominal viscera are supplied by a large 
prevertebral plexus 

Regional anatomy 

Surface topography 

Four-quadrant pattern 
Nine-region pattern 






Abdominal wall 280 

Superficial fascia 280 
Anterolateral muscles 282 

Extraperitoneal fascia 288 

Peritoneum 288 
Innervation 289 

Arterial supply and venous drainage 291 
Lymphatic drainage 292 
Groin 292 

Inguinal canal 294 
Inguinal hernias 299 
Abdominal viscera 303 
Peritoneum 303 
Peritoneal cavity 304 
Organs 310 
Arterial supply 343 
Venous drainage 354 
Lymphatics 358 
Innervation 358 

Posterior abdominal region 366 
Posterior abdominal wall 367 
Viscera 373 


Vasculature 387 
Lymphatic system 392 
Nervous system in the posterior abdominal 
region 394 

Sympathetic trunks and splanchnic nerves 394 
Surface anatomy 402 

Abdomen surface anatomy 402 
Defining the surface projection of the 
abdomen 402 

How to find the superficial inguinal ring 403 
How to determine lumbar vertebral levels 404 
Visualizing structures at the LI vertebral level 405 
Visualizing the position of major blood 
vessels 406 

Using abdominal quadrants to locate major 
viscera 407 

Defining surface regions to which pain from the gut 
is referred 408 
Where to find the kidneys 409 
Where to find the spleen 409 


Clinical cases 410 








Conceptual overview • General Description 



Conceptual overview 

GENERAL DESCRIPTION 


The abdomen is a roughly cylindrical chamber extending 
from the inferior margin of the thorax to the superior 
margin of the pelvis and the lower limb (Fig. 4.1 A). 

The inferior thoracic aperture forms the superior 
opening to the abdomen, and is closed by the diaphragm. 
Interiorly, the deep abdominal wall is continuous with the 


pelvic wall at the pelvic inlet. Superficially, the inferior 
limit of the abdominal wall is the superior margin of the 
lower limb. 

The chamber enclosed by the abdominal wall contains 
a single large peritoneal cavity, which freely communi¬ 
cates with the pelvic cavity. 



Fig. 4.1 Abdomen. A. Boundaries. 


255 






















Abdomen 



Costal margin 


Left kidney 


Fig. 4.1, cont’d B. Arrangement of abdominal contents. Inferior view. 


Abdominal viscera are either suspended in the perito¬ 
neal cavity by mesenteries or positioned between the cavity 

and the musculoskeletal wall (Fig. 4.IB). 

Abdominal viscera include: 

■ major elements of the gastrointestinal system—the 
caudal end of the esophagus, stomach, small and large 
intestines, liver, pancreas, and gallbladder; 

■ the spleen; 

■ components of the urinary system—kidneys and 
ureters; 

■ the suprarenal glands; and 

■ major neurovascular structures. 


FUNCTIONS 

Houses and protects major viscera 

The abdomen houses major elements of the gastrointesti¬ 
nal system (Fig. 4.2), the spleen, and parts of the urinary 
system. 

Much of the liver, gallbladder, stomach, and spleen and 
parts of the colon are under the domes of the diaphragm, 
which project superiorly above the costal margin of the 
thoracic wall, and as a result these abdominal viscera are 
protected by the thoracic wall. The superior poles of the 
kidneys are deep to the lower ribs. 

Viscera not under the domes of the diaphragm are sup¬ 
ported and protected predominantly by the muscular walls 
of the abdomen. 


256 





















Conceptual overview • Functions 



Fig. 4.2 The abdomen contains and protects the abdominal viscera. 























258 


Abdomen 



Inspiration 

Fig. 43 The abdomen assists in breathing. 



Expiration 


Diaphragm 


Relaxation of 
diaphragm 


Contraction of 

abdominal 

muscles 


Breathing 

One of the most important roles of the abdominal wall is 
to assist in breathing: 

■ It relaxes during inspiration to accommodate expansion 
of the thoracic cavity and the inferior displacement of 
abdominal viscera during contraction of the diaphragm 
(Fig. 4.3). 

■ During expiration, it contracts to assist in elevating 
the domes of the diaphragm, thus reducing thoracic 
volume. 

Material can be expelled from the airway by forced expi¬ 
ration using the abdominal muscles, as in coughing or 
sneezing. 

Changes in intraabdominal pressure 

Contraction of abdominal wall muscles can dramatically 
increase intraabdominal pressure when the diaphragm is 



Fig. 4.4 Increasing intraabdominal pressure to assist in 
micturition, defecation, and childbirth. 


in a fixed position (Fig. 4.4). Air is retained in the lungs by 
closing valves in the larynx in the neck. Increased intra¬ 
abdominal pressure assists in voiding the contents of the 
bladder and rectum and in giving birth. 
























Conceptual overview • Component Parts 



COMPONENT PARTS 

Wall 

The abdominal wall consists partly of bone but mainly 

of muscle (Fig. 4.5). The skeletal elements of the wall 

(Fig. 4.5A) are: 

■ the five lumbar vertebrae and their intervening inter¬ 
vertebral discs, 

■ the superior expanded parts of the pelvic bones, and 

■ bony components of the inferior thoracic wall, includ¬ 
ing the costal margin, rib XII, the end of rib XI, and the 
xiphoid process. 


Muscles make up the rest of the abdominal wall 

(Fig. 4.5B): 

■ Lateral to the vertebral column, the quadratus lumbo- 
rum, psoas major, and iliacus muscles reinforce the pos¬ 
terior aspect of the wall. The distal ends of the psoas 
major and iliacus muscles pass into the thigh and are 
major flexors of the hip joint. 

■ Lateral parts of the abdominal wall are predominantly 
formed by three layers of muscles, which are similar in 
orientation to the intercostal muscles of the thorax— 
transversus abdominis, internal oblique, and external 
oblique. 




Pelvic inlet 


Quadratus 

lumborum 


Rectus 

abdominis 


Inguinal ligament Gap between inguinal 

ligament and pelvic bone 


Psoas 


Iliacus 


Costal margin 


External oblique 


Internal 

Transversus 


major 


Rib XII 


Iliolumbar 

ligament 


Fig. 4.5 Abdominal wall. A. Skeletal elements. B. Muscles. 


259 

















Abdomen 


■ Anteriorly, a segmented muscle (the rectus abdominis) 
on each side spans the distance between the inferior 
thoracic wall and the pelvis. 

Structural continuity between posterior, lateral, and 
anterior parts of the abdominal wall is provided by 
thick fascia posteriorly and by flat tendinous sheets 
(aponeuroses) derived from muscles of the lateral wall. A 
fascial layer of varying thickness separates the abdominal 
wall from the peritoneum, which lines the abdominal 
cavity. 


Abdominal cavity 

The general organization of the abdominal cavity is one 
in which a central gut tube (gastrointestinal system) is 
suspended from the posterior abdominal wall and partly 
from the anterior abdominal wall by thin sheets of tissue 
(mesenteries; Fig. 4.6): 

■ a ventral (anterior) mesentery for proximal regions of 
the gut tube; 

■ a dorsal (posterior) mesentery along the entire length of 
the system. 

Different parts of these two mesenteries are named 
according to the organs they suspend or with which they 
are associated. 

Major viscera, such as the kidneys, that are not sus¬ 
pended in the abdominal cavity by mesenteries are associ¬ 
ated with the abdominal wall. 

The abdominal cavity is lined by peritoneum, which 
consists of an epithelial-like single layer of cells (the meso- 
thelium) together with a supportive layer of connective 
tissue. Peritoneum is similar to the pleura and serous peri¬ 
cardium in the thorax. 

The peritoneum reflects off the abdominal wall to 
become a component of the mesenteries that suspend the 
viscera. 

■ Parietal peritoneum lines the abdominal wall. 

■ Visceral peritoneum covers suspended organs. 

Normally, elements of the gastrointestinal tract and 
its derivatives completely fill the abdominal cavity, 
making the peritoneal cavity a potential space, and 
visceral peritoneum on organs and parietal peritoneum 
on the adjacent abdominal wall slide freely against one 
another. 

Abdominal viscera are either intraperitoneal or 
retroperitoneal: 


Branch of aorta 
Gastrointestinal tract 


Aorta 



Ventral mesentery 


Kidney—posterior to 
peritoneum 


Dorsal mesentery 


Parietal peritoneum 


Visceral peritoneum 


Fig. 4.6 The gut tube is suspended by mesenteries. 


■ Intraperitoneal structures, such as elements of the 
gastrointestinal system, are suspended from the abdom¬ 
inal wall by mesenteries; 

■ Structures that are not suspended in the abdominal 
cavity by a mesentery and that lie between the parietal 
peritoneum and abdominal wall are retroperitoneal 
in position. 

Retroperitoneal structures include the kidneys and 
ureters, which develop in the region between the perito¬ 
neum and the abdominal wall and remain in this position 
in the adult. 

During development, some organs, such as parts of the 
small and large intestines, are suspended initially in the 
abdominal cavity by a mesentery, and later become retro¬ 
peritoneal secondarily by fusing with the abdominal wall 
(Fig. 4.7). 































Conceptual overview • Component Parts 


Visceral peritoneum 





Gastrointestinal tract 


Secondary retroperitoneal part of gastrointestinal tract 


Gastrointestinal tract 


Mesentery 

A 


Retroperitoneal structures 
Parietal peritoneum 

Intraperitoneal part of gastrointestinal tract 


Gastrointestinal tract 
Mesentery before fusion with wall 


Artery to gastrointestinal tract 


Fig. 4.7 A series showing the progression (A to C) from an intraperitoneal organ to a secondarily retroperitoneal organ. 












































Abdomen 


Large vessels, nerves, and lymphatics are associated 
with the posterior abdominal wall along the median axis 
of the body in the region where, during development, the 
peritoneum reflects off the wall as the dorsal mesentery, 
which supports the developing gut tube. As a consequence, 
branches of the neurovascular structures that pass to parts 
of the gastrointestinal system are unpaired, originate from 
the anterior aspects of their parent structures, and travel 
in mesenteries or pass retroperitoneally in areas where the 
mesenteries secondarily fuse to the wall. 

Generally, vessels, nerves, and lymphatics to the abdom¬ 
inal wall and to organs that originate as retroperitoneal 
structures branch laterally from the central neurovascular 
structures and are usually paired, one on each side. 

Inferior thoracic aperture 

The superior aperture of the abdomen is the inferior 
thoracic aperture, which is closed by the diaphragm (see 


pp. 126-127). The margin of the inferior thoracic aperture 
consists of vertebra TXII, rib XII, the distal end of rib XI, 
the costal margin, and the xiphoid process of the sternum. 

Diaphragm 

The musculotendinous diaphragm separates the abdomen 
from the thorax. 

The diaphragm attaches to the margin of the inferior 
thoracic aperture, but the attachment is complex posteri¬ 
orly and extends into the lumbar area of the vertebral 
column (Fig. 4.8). On each side, a muscular extension 
(crus) firmly anchors the diaphragm to the anterolateral 
surface of the vertebral column as far down as vertebra LIII 
on the right and vertebra LII on the left. 

Because the costal margin is not complete posteriorly, 
the diaphragm is anchored to arch-shaped (arcuate) liga¬ 
ments, which span the distance between available bony 
points and the intervening soft tissues: 


Lateral arcuate 
ligament 





IIV/ f 



fl 

1 / 

j 

J / 



Esophageal opening 
Costal margin 

Median arcuate ligament 


Medial arcuate ligament 


Left crus 

Quadratus lumborum 


Psoas major 


262 


Fig. 4.8 Inferior thoracic aperture and the diaphragm. 

















Conceptual overview • Relationship to Other Regions 


■ Medial and lateral arcuate ligaments cross muscles 
of the posterior abdominal wall and attach to vertebrae, 
the transverse processes of vertebra LI and rib XII, 
respectively. 

■ A median arcuate ligament crosses the aorta and is 
continuous with the crus on each side. 

The posterior attachment of the diaphragm extends 
much farther inferiorly than the anterior attachment. Con¬ 
sequently, the diaphragm is an important component of 
the posterior abdominal wall, to which a number of viscera 
are related. 

Pelvic inlet 

The abdominal wall is continuous with the pelvic wall at 
the pelvic inlet, and the abdominal cavity is continuous 
with the pelvic cavity. 

The circular margin of the pelvic inlet is formed entirely 
by bone: 

■ posteriorly by the sacrum, 

■ anteriorly by the pubic symphysis, and 

■ laterally, on each side, by a distinct bony rim on the 
pelvic bone (Fig. 4.9). 

Because of the way in which the sacrum and attached 
pelvic bones are angled posteriorly on the vertebral column, 
the pelvic cavity is not oriented in the same vertical plane 
as the abdominal cavity. Instead, the pelvic cavity projects 
posteriorly, and the inlet opens anteriorly and somewhat 
superiorly (Fig. 4.10). 

RELATIONSHIP TO O THER RE GIONS 
Thorax 

The abdomen is separated from the thorax by the dia¬ 
phragm. Structures pass between the two regions through 
or posterior to the diaphragm (see Fig. 4.8). 

Pelvis 

The pelvic inlet opens directly into the abdomen and struc¬ 
tures pass between the abdomen and pelvis through it. 

The peritoneum lining the abdominal cavity is continu¬ 
ous with the peritoneum in the pelvis. Consequently, the 



Fig. 4.9 Pelvic inlet. 



Fig. 4.10 Orientation of abdominal and pelvic cavities. 


























Abdomen 



Pelvic inlet 


Shadow of ureter 


Peritoneum 


Bladder 

Uterus 

Fig. 4.11 The abdominal cavity is continuous with the pelvic cavity. 


Rectum 


Shadow of internal 
iliac vessels 


abdominal cavity is entirely continuous with the pelvic 
cavity (Fig. 4.11). Infections in one region can therefore 
freely spread into the other. 

The bladder expands superiorly from the pelvic cavity 
into the abdominal cavity and, during pregnancy, the 
uterus expands freely superiorly out of the pelvic cavity 
into the abdominal cavity. 

Lower limb 

The abdomen communicates directly with the thigh 
through an aperture formed anteriorly between the infe¬ 
rior margin of the abdominal wall (marked by the inguinal 


ligament) and the pelvic bone (Fig. 4.12). Structures that 
pass through this aperture are: 

■ the major artery and vein of the lower limb; 

■ the femoral nerve, which innervates the quadriceps 
femoris muscle, which extends the knee; 

■ lymphatics; and 

■ the distal ends of psoas major and iliacus muscles, 
which flex the thigh at the hip joint. 

As vessels pass inferior to the inguinal ligament, their 
names change—the external iliac artery and vein of the 
abdomen become the femoral artery and vein of the thigh. 


264 



































Conceptual overview • Key Features 



Fig. 4.12 Structures passing between the abdomen and thigh. 

KEY FEATURES 

Arrangement of abdominal viscera 
in the adult 

A basic knowledge of the development of the gastrointes¬ 
tinal tract is needed to understand the arrangement of 
viscera and mesenteries in the abdomen (Fig. 4.13). 

The early gastrointestinal tract is oriented longitudi¬ 
nally in the body cavity and is suspended from surrounding 
walls by a large dorsal mesentery and a much smaller 
ventral mesentery. 

Superiorly, the dorsal and ventral mesenteries are 
anchored to the diaphragm. 

The primitive gut tube consists of the foregut, the 
midgut, and the hindgut. Massive longitudinal growth of 
the gut tube, rotation of selected parts of the tube, and 
secondary fusion of some viscera and their associated mes¬ 
enteries to the body wall participate in generating the adult 
arrangement of abdominal organs. 

Development of the foregut 

In abdominal regions, the foregut gives rise to the distal 
end of the esophagus, the stomach, and the proximal part 
of the duodenum. The foregut is the only part of the gut 


tube suspended from the wall by both the ventral and 
dorsal mesenteries. 

A diverticulum from the anterior aspect of the foregut 
grows into the ventral mesentery, giving rise to the liver 
and gallbladder, and, ultimately, to the ventral part of the 
pancreas. 

The dorsal part of the pancreas develops from an out¬ 
growth of the foregut into the dorsal mesentery. The spleen 
develops in the dorsal mesentery in the region between the 
body wall and presumptive stomach. 

In the foregut, the developing stomach rotates clockwise 
and the associated dorsal mesentery, containing the spleen, 
moves to the left and greatly expands. During this process, 
part of the mesentery becomes associated with, and sec¬ 
ondarily fuses with, the left side of the body wall. 

At the same time, the duodenum, together with its 
dorsal mesentery and an appreciable part of the pancreas, 
swings to the right and fuses to the body wall. 

Secondary fusion of the duodenum to the body wall, 
massive growth of the liver in the ventral mesentery, and 
fusion of the superior surface of the liver to the diaphragm 
restrict the opening to the space enclosed by the ballooned 
dorsal mesentery associated with the stomach. This 
restricted opening is the omental foramen (epiploic 
foramen). 

The part of the abdominal cavity enclosed by the 
expanded dorsal mesentery, and posterior to the stomach, 
is the omental bursa (lesser sac). Access, through the 
omental foramen, to this space from the rest of the perito¬ 
neal cavity (greater sac) is inferior to the free edge of the 
ventral mesentery. 

Part of the dorsal mesentery that initially forms part of 
the lesser sac greatly enlarges in an inferior direction, and 
the two opposing surfaces of the mesentery fuse to form an 
apron-like structure (the greater omentum). The greater 
omentum is suspended from the greater curvature of the 
stomach, lies over other viscera in the abdominal cavity, 
and is the first structure observed when the abdominal 
cavity is opened anteriorly. 

Development of the midgut 

The midgut develops into the distal part of the duodenum 
and the jejunum, ileum, ascending colon, and proximal 
two-thirds of the transverse colon. A small yolk sac proj¬ 
ects anteriorly from the developing midgut into the 
umbilicus. 

Rapid growth of the gastrointestinal system results in a 
loop of the midgut herniating out of the abdominal cavity 
and into the umbilical cord. As the body grows in size and 
the connection with the yolk sac is lost, the midgut returns 
to the abdominal cavity. While this process is occurring, 
the two limbs of the midgut loop rotate counterclockwise 265 











Abdomen 


Stomach 



Liver 


Dorsal pancreatic bud 


Dorsal 

mesentery 


Superior 

mesenteric 

artery 


Colon 


Gallbladder 
Ventral pancreatic bud 


Yolk sac 


Superior 

mesenteric artery 

B 


Liver 




Superior 
mesenteric 
artery 


Stomach 


Cecum 

D 


Greater 

omentum 


Liver 


Omental 

foramen 


Stomach 


Fig. 4.13 A series (A to H) showing the development of the gut and mesenteries. 


266 









































Conceptual overview • Key Features 




Liver 


Spleen 


Stomach 


Developing greater omentum 


Liver 


Omental bursa 


Greater 

omentum 


Cecum 

F 



Fig. 4.13, cont’d 











































Abdomen 


around their combined central axis, and the part of the 
loop that becomes the cecum descends into the inferior 
right aspect of the cavity. The superior mesenteric artery, 
which supplies the midgut, is at the center of the axis of 
rotation. 

The cecum remains intraperitoneal, the ascending 
colon fuses with the body wall becoming secondarily retro¬ 
peritoneal, and the transverse colon remains suspended by 
its dorsal mesentery (transverse mesocolon). The greater 
omentum hangs over the transverse colon and the meso¬ 
colon and usually fuses with these structures. 

Development of the hindgut 

The distal one-third of the transverse colon, descending 
colon, sigmoid colon, and superior part of the rectum 
develop from the hindgut. 

Proximal parts of the hindgut swing to the left and 
become the descending colon and sigmoid colon. The 
descending colon and its dorsal mesentery fuse to the body 
wall, while the sigmoid colon remains intraperitoneal. The 
sigmoid colon passes through the pelvic inlet and is con¬ 
tinuous with the rectum at the level of vertebra Sill. 

Skin and muscles of the anterior 
and lateral abdominal wall 
and thoracic intercostal nerves 

The anterior rami of thoracic spinal nerves T7 to T12 
follow the inferior slope of the lateral parts of the ribs 
and cross the costal margin to enter the abdominal 
wall (Fig. 4.14). Intercostal nerves T7 to Til supply 
skin and muscle of the abdominal wall, as does the subcos¬ 
tal nerve T12. In addition, T5 and T6 supply upper parts 
of the external oblique muscle of the abdominal wall; 
T6 also supplies cutaneous innervation to skin over the 
xiphoid. 

Skin and muscle in the inguinal and suprapubic regions 
of the abdominal wall are innervated by LI and not by 
thoracic nerves. 



Dermatomes of the anterior abdominal wall are indi¬ 
cated in Figure 4.14. In the midline, skin over the infraster- 
nal angle is T6 and that around the umbilicus is T10. LI 
innervates skin in the inguinal and suprapubic regions. 

Muscles of the abdominal wall are innervated segmen- 
tally in patterns that generally reflect the patterns of the 
overlying dermatomes. 


268 


















Conceptual overview • Key Features 



The groin is a weak area in the anterior 
abdominal wall 

During development, the gonads in both sexes descend 
from their sites of origin on the posterior abdominal wall 
into the pelvic cavity in women and the developing scrotum 
in men (Fig. 4.15). 

Before descent, a cord of tissue (the gubernaculum) 
passes through the anterior abdominal wall and connects 
the inferior pole of each gonad with primordia of the 
scrotum in men and the labia majora in women (labioscro- 
tal swellings). 

A tubular extension (the processus vaginalis) of the 
peritoneal cavity and the accompanying muscular layers 
of the anterior abdominal wall project along the guber¬ 
naculum on each side into the labioscrotal swellings. 

In men, the testis, together with its neurovascular struc¬ 
tures and its efferent duct (the ductus deferens) descends 
into the scrotum along a path, initially defined by the 
gubernaculum, between the processus vaginalis and the 
accompanying coverings derived from the abdominal wall. 


All that remains of the gubernaculum is a connective 
tissue remnant that attaches the caudal pole of the testis 
to the scrotum. 

The inguinal canal is the passage through the 
anterior abdominal wall created by the processus vagina¬ 
lis. The spermatic cord is the tubular extension of the 
layers of the abdominal wall into the scrotum that con¬ 
tains all structures passing between the testis and the 
abdomen. 

The distal sac-like terminal end of the spermatic cord on 
each side contains the testis, associated structures, and the 
now isolated part of the peritoneal cavity (the cavity of the 
tunica vaginalis). 

In women, the gonads descend to a position just inside 
the pelvic cavity and never pass through the anterior 
abdominal wall. As a result, the only major structure 
passing through the inguinal canal is a derivative of the 
gubernaculum (the round ligament of the uterus). 

In both men and women, the groin (inguinal region) is 
a weak area in the abdominal wall (Fig. 4.15) and is the 
site of inguinal hernias. 



Urogenital membrane 

A 


Genital tubercle 


Labioscrotal swelling 


Processus vaginalis 


Gonad 


Muscle wall 


Gubernaculum 


Fig. 4.15 Inguinal region. A. Development. 


269 













Abdomen 


Inferior vena cava 


Right testicular artery 
Right testicular vein 


Superficial 
inguinal ring 

Spermatic cord 


Remnant of 
gubernaculum 


Inferior vena cava 

Aorta 


Uterus 


Superficial 
inguinal ring 



Aorta 

Left testicular vein 
Left testicular artery 


Pelvic brim 
Left ductus deferens 
Deep inguinal ring 
Inguinal canal 


Ductus deferens 

Testicular 
artery and vein 



Tunica vaginalis 


Left renal artery 

Left renal vein 
Left ovarian vein 

Left ovarian artery 


Pelvic inlet 


Uterine tube 

Round ligament 
of uterus (remnants 
of gubernaculum) 


Fig. 4.15, cont'd B. In men. C. In women. 






















































Conceptual overview • Key Features 


Vertebral level LI 

The transpyloric plane is a horizontal plane that tran¬ 
sects the body through the lower aspect of vertebra LI 
(Fig. 4.16). It: 

■ is about midway between the jugular notch and the 
pubic symphysis, and crosses the costal margin on each 
side at roughly the ninth costal cartilage; 

■ crosses through the opening of the stomach into the 
duodenum (the pyloric orifice), which is just to the right 
of the body of LI; the duodenum then makes a charac¬ 
teristic C-shaped loop on the posterior abdominal wall 
and crosses the midline to open into the jejunum just to 
the left of the body of vertebra LII, whereas the head of 
the pancreas is enclosed by the loop of the duodenum, 
and the body of the pancreas extends across the midline 
to the left; 

■ crosses through the body of the pancreas; and 

■ approximates the position of the hila of the kidneys; 
though because the left kidney is slightly higher than 
the right, the transpyloric plane crosses through the 
inferior aspect of the left hilum and the superior part of 
the right hilum. 

The gastrointestinal system and its 
derivatives are supplied by 
three major arteries 

Three large unpaired arteries branch from the anterior 
surface of the abdominal aorta to supply the abdominal 
part of the gastrointestinal tract and all of the structures 
(liver, pancreas, and gallbladder) to which this part of the 
gut gives rise during development (Fig. 4.17). These 
arteries pass through derivatives of the dorsal and ventral 
mesenteries to reach the target viscera. These vessels 
therefore also supply structures such as the spleen and 
lymph nodes that develop in the mesenteries. These three 
arteries are: 

■ the celiac artery, which branches from the abdominal 
aorta at the upper border of vertebra LI and supplies the 
foregut; 


Pyloric orifice between 
stomach and duodenum 



Fig. 4.16 Vertebral level LI. 


■ the superior mesenteric artery, which arises from 
the abdominal aorta at the lower border of vertebra LI 
and supplies the midgut; and 

■ the inferior mesenteric artery, which branches from 
the abdominal aorta at approximately vertebral level 
LIII and supplies the hindgut. 

























Abdomen 


Foregut 


Midgut 


Hindgut 


A 



Inferior vena cava 


Superior mesenteric artery 


Aorta 


Inferior mesenteric 
artery 


Celiac trunk 


Superior mesenteric artery 


Inferior mesenteric artery 


Celiac trunk 


Fig. 4.17 Blood supply of the gut. A. Relationship of vessels to the gut and mesenteries. B. Anterior view. 


272 









































Conceptual overview • Key Features 



Venous shunts from left to right 

All blood returning to the heart from regions of the body 
other than the lungs flows into the right atrium of the 
heart. The inferior vena cava is the major systemic vein in 
the abdomen and drains this region together with the 
pelvis, perineum, and both lower limbs (Fig. 4.18). 

The inferior vena cava lies to the right of the vertebral 
column and penetrates the central tendon of the 


diaphragm at approximately vertebral level TVIII. A 
number of large vessels cross the midline to deliver 
blood from the left side of the body to the inferior vena 
cava. 

■ One of the most significant is the left renal vein, which 
drains the kidney, suprarenal gland, and gonad on the 
same side. 



Right suprarenal vein 


Superior vena cava 


Right atrium 


Right gonadal vein 


Heart 


Diaphragm 


Left suprarenal vein 
Left renal vein 


Left gonadal vein 
Left lumbar vein 


Left common iliac vein 


Pelvic inlet 


Fig. 4.18 Left-to-right venous shunts. 


273 
































Abdomen 


■ Another is the left common iliac vein, which crosses the 
midline at approximately vertebral level LV to join with 
its partner on the right to form the inferior vena cava. 
These veins drain the lower limbs, the pelvis, the 
perineum, and parts of the abdominal wall. 

■ Other vessels crossing the midline include the left lumbar 
veins, which drain the back and posterior abdominal 
wall on the left side. 


All venous drainage from the 
gastrointestinal system passes 
through the liver 

Blood from abdominal parts of the gastrointestinal 
system and the spleen passes through a second vascular 
bed, in the liver, before ultimately returning to the heart 
(Fig. 4.19). 



Hepatic portal vein 


Umbilicus 


Hepatic veins 


Esophagus 


Rectum 


274 


Fig. 4.19 Hepatic portal system. 


















Conceptual overview • Key Features 


Venous blood from the digestive tract, pancreas, gall¬ 
bladder, and spleen enters the inferior surface of the liver 
through the large hepatic portal vein. This vein then 
ramifies like an artery to distribute blood to small 
endothelial-lined hepatic sinusoids, which form the vascu¬ 
lar exchange network of the liver. 

After passing through the sinusoids, the blood collects 
in a number of short hepatic veins, which drain into the 
inferior vena cava just before the inferior vena cava pene¬ 
trates the diaphragm and enters the right atrium of the 
heart. 

Normally, vascular beds drained by the hepatic portal 
system interconnect, through small veins, with beds 
drained by systemic vessels, which ultimately connect 
directly with either the superior or inferior vena cava. 

Portacaval anastomoses 

Among the clinically most important regions of overlap 
between the portal and caval systems are those at each end 
of the abdominal part of the gastrointestinal system: 

■ around the inferior end of the esophagus; 

■ around the inferior part of the rectum. 

Small veins that accompany the degenerate umbilical 
vein (round ligament of the liver) establish another 
important portacaval anastomosis. 

The round ligament of the liver connects the umbilicus 
of the anterior abdominal wall with the left branch of the 


portal vein as it enters the liver. The small veins that accom¬ 
pany this ligament form a connection between the portal 
system and para-umbilical regions of the abdominal wall, 
which drain into systemic veins. 

Other regions where portal and caval systems inter¬ 
connect include: 

■ where the liver is in direct contact with the diaphragm 
(the bare area of the liver); 

■ where the wall of the gastrointestinal tract is in direct 
contact with the posterior abdominal wall (retroperito¬ 
neal areas of the large and small intestine); and 

■ the posterior surface of the pancreas (much of the pan¬ 
creas is secondarily retroperitoneal). 

Blockage of the hepatic portal vein or of vascular 
channels in the liver 

Blockage of the hepatic portal vein or of vascular chan¬ 
nels in the liver can affect the pattern of venous return 
from abdominal parts of the gastrointestinal system. 
Vessels that interconnect the portal and caval systems 
can become greatly enlarged and tortuous, allowing 
blood in tributaries of the portal system to bypass the 
liver, enter the caval system, and thereby return to the 
heart. Portal hypertension can result in esophageal and 
rectal varices and in caput medusae in which systemic 
vessels that radiate from para-umbilical veins enlarge and 
become visible on the abdominal wall. 


Abdomen 


Abdominal viscera are supplied by a large 
prevertebral plexus 

Innervation of the abdominal viscera is derived from a 
large prevertebral plexus associated mainly with the ante¬ 
rior and lateral surfaces of the aorta (Fig. 4.20). Branches 
are distributed to target tissues along vessels that originate 
from the abdominal aorta. 


The prevertebral plexus contains sympathetic, para¬ 
sympathetic, and visceral sensory components: 

■ Sympathetic components originate from spinal cord 
levels T5 to L2. 

■ Parasympathetic components are from the vagus nerve 
[X] and spinal cord levels S2 to S4. 

■ Visceral sensory fibers generally parallel the motor 
pathways. 


Sympathetic input 


Greater, lesser, and least 
splanchnic nerves 
(T5 to T12) 


Lumbar splanchnic 
nerves (LI, L2) 


Prevertebral plexus 



Parasympathetic input 


Anterior and posterior 
vagus trunks (cranial) 


Pelvic splanchnic 
nerves (S2 to S4) 


Fig. 4.20 Prevertebral plexus. 

















Regional anatomy • Surface Topography 



Regional anatomy 

The abdomen is the part of the trunk inferior to the 
thorax (Fig. 4.21). Its musculomembranous walls sur¬ 
round a large cavity (the abdominal cavity), which is 
bounded superiorly by the diaphragm and inferiorly by the 
pelvic inlet. 

The abdominal cavity may extend superiorly as high as 
the fourth intercostal space, and is continuous inferiorly 
with the pelvic cavity. It contains the peritoneal cavity 
and the abdominal viscera. 

SURFACE TOPOGRAPHY 

Topographical divisions of the abdomen are used to 
describe the location of abdominal organs and the pain 


associated with abdominal problems. The two schemes 
most often used are: 

■ a four-quadrant pattern and 

■ a nine-region pattern. 

Four-quadrant pattern 

A horizontal transumbilical plane passing through the 
umbilicus and the intervertebral disc between vertebrae 
LIII and LIV and intersecting with the vertical median 
plane divides the abdomen into four quadrants—the 
right upper, left upper, right lower, and left lower quadrants 
(Fig. 4.22). 



Sternum 

Diaphragm 

Abdominal cavity 

Pelvic inlet 

Pelvic cavity 
Pubic symphysis 


Fig. 4.21 Boundaries of the abdominal cavity. 





Transumbilical plane Median plane 
Fig. 4.22 Four-quadrant topographical pattern. 


277 





































278 


Abdomen 


Nine-region pattern 

The nine-region pattern is based on two horizontal and two 

vertical planes (Fig. 4.23). 

■ The superior horizontal plane (the subcostal plane) is 
immediately inferior to the costal margins, which places 
it at the lower border of the costal cartilage of rib X and 
passing posteriorly through the body of vertebra LIII. 
(Note, however, that sometimes the transpyloric 
plane, halfway between the jugular notch and the sym¬ 
physis pubis or halfway between the umbilicus and the 
inferior end of the body of the sternum, passing poste¬ 
riorly through the lower border of vertebra LI and inter¬ 
secting with the costal margin at the ends of the ninth 
costal cartilages, is used instead.) 

■ The inferior horizontal plane (the intertubercular 
plane) connects the tubercles of the iliac crests, which 


Subcostal plane Midclavicular planes 



Intertubercular plane 


Fig. 4.23 Nine-region organizational pattern. 


are palpable structures 5 cm posterior to the anterior 
superior iliac spines, and passes through the upper part 
of the body of vertebra LV. 

■ The vertical planes pass from the midpoint of the clavi¬ 
cles inferiorly to a point midway between the anterior 
superior iliac spine and pubic symphysis. 

These four planes establish the topographical divisions 
in the nine-region organization. The following designa¬ 
tions are used for each region: superiorly the right 
hypochondrium, the epigastric region, and the left hypo- 
chondrium; inferiorly the right groin (inguinal region), 
pubic region, and left groin (inguinal region); and in the 
middle the right flank (lateral region), the umbilical region, 
and the left flank (lateral region) (Fig. 4.23). 


In the clinic 

Surgical incisions 

Access to the abdomen and its contents is usually 
obtained through incisions in the anterior abdominal 
wall. Traditionally, incisions have been placed at and 
around the region of surgical interest. The size of these 
incisions was usually large to allow good access and 
optimal visualization of the abdominal cavity. As 
anesthesia has developed and muscle-relaxing drugs 
have become widely used, the abdominal incisions have 
become smaller. 

Currently, the most commonly used large abdominal 
incision is a central craniocaudad incision from the 
xiphoid process to the symphysis pubis, which provides 
wide access to the whole of the abdominal contents 
and allows an exploratory procedure to be performed 
(laparotomy). 




















Regional anatomy • Surface Topography 


In the clinic 
Laparoscopic surgery 

Laparoscopic surgery, also known as minimally invasive 
or keyhole surgery, is performed by operating through a 
series of small incisions no more than 1 to 2 cm in length. 
As the incisions are much smaller than those used in 
traditional abdominal surgery, patients experience less 
postoperative pain and have shorter recovery times. There 
is also a favorable cosmetic outcome with 
smaller scars. Several surgical procedures such as 
appendicectomy, cholecystectomy, and hernia repair, 
as well as numerous orthopaedic, urological, and 
gynecological procedures, are now commonly 
performed laparoscopically. 

During the operation, a camera known as a 
laparoscope is used to transmit live, magnified images 
of the surgical field to a monitor viewed by the surgeon. 
The camera is inserted into the abdominal cavity through 
a small incision, called a port-site, usually atthe umbilicus. 
In order to create enough space to operate, the 
abdominal wall is elevated by inflating the cavity with gas, 
typically carbon dioxide. Other long, thin surgical 
instruments are then introduced through additional 
port-sites, which can be used by the surgeon 


to operate. The placement of these port-sites is carefully 
planned to allow optimal access to the surgical field. 

Laparoscopic surgery has been further enhanced with 
the use of surgical robots. Using these systems the 
surgeon moves the surgical instruments indirectly by 
controlling robotic arms, which are inserted into the 
operating field through small incisions. Robot-assisted 
surgery is now routinely used worldwide and has helped 
overcome some of the limitations of laparoscopy by 
enhancing the surgeon's dexterity. The robotic system is 
precise, provides the surgeon with a 3D view of the 
surgical field, and allows improved degree of rotation and 
manipulation of the surgical instruments. Several 
procedures such as prostatectomy and cholecystectomy 
can now be performed with this method. 

Laparoendoscopic single-site surgery, also known as 
single-port laparoscopy, is the most recent advance in 
laparoscopic surgery. This method uses a single incision, 
usually umbilical, to introduce a port with several 
operating channels and can be performed with or without 
robotic assistance. Benefits include less postoperative 
pain, a faster recovery time, and an even better cosmetic 
result than traditional laparoscopic surgery. 


Abdomen 


ABDOMINAL WALL 

The abdominal wall covers a large area. It is bounded supe¬ 
riorly by the xiphoid process and costal margins, posteri¬ 
orly by the vertebral column, and inferiorly by the upper 
parts of the pelvic bones. Its layers consist of skin, superfi¬ 
cial fascia (subcutaneous tissue), muscles and their associ¬ 
ated deep fascias, extraperitoneal fascia, and parietal 
peritoneum (Fig. 4.24). 

Superficial fascia 

The superficial fascia of the abdominal wall (subcutaneous 
tissue of abdomen) is a layer of fatty connective tissue. It is 
usually a single layer similar to, and continuous with, the 
superficial fascia throughout other regions of the body. 
However, in the lower region of the anterior part of the 
abdominal wall, below the umbilicus, it forms two layers: 
a superficial fatty layer and a deeper membranous layer. 

Superficial layer 

The superficial fatty layer of superficial fascia (Camper’s 
fascia) contains fat and varies in thickness (Figs. 4.25 and 
4.26). It is continuous over the inguinal ligament with the 
superficial fascia of the thigh and with a similar layer in 
the perineum. 


In men, this superficial layer continues over the penis 
and, after losing its fat and fusing with the deeper layer of 
superficial fascia, continues into the scrotum where it 
forms a specialized fascial layer containing smooth muscle 
fibers (the dartos fascia). In women, this superficial layer 
retains some fat and is a component of the labia majora. 

Deeper layer 

The deeper membranous layer of superficial fascia (Scar¬ 
pa’s fascia) is thin and membranous, and contains little 
or no fat (Fig. 4.25). Inferiorly, it continues into the thigh, 
but just below the inguinal ligament, it fuses with the deep 
fascia of the thigh (the fascia lata; Fig. 4.26). In the 
midline, it is firmly attached to the linea alba and the sym¬ 
physis pubis. It continues into the anterior part of the 
perineum where it is firmly attached to the ischiopubic 
rami and to the posterior margin of the perineal mem¬ 
brane. Here, it is referred to as the superficial perineal 
fascia (Colles’ fascia). 

In men, the deeper membranous layer of superficial 
fascia blends with the superficial layer as they both pass 
over the penis, forming the superficial fascia of the penis, 
before they continue into the scrotum where they form the 
dartos fascia (Fig. 4.25). Also in men, extensions of the 
deeper membranous layer of superficial fascia attached to 
the pubic symphysis pass inferiorly onto the dorsum and 


Superficial fascia— 
fatty layer 
(Camper's fascia) 


Superficial fascia— 
membranous layer 
(Scarpa's fascia) 



External oblique muscle 


Internal oblique muscle 


Transversus 
abdominis muscle 

Transversalis fascia 


Parietal peritoneum 


Fig. 4.24 Layers of the abdominal wall. 


Extraperitoneal fascia 























Regional anatomy • Abdominal Wall 





Fig. 4.25 Superficial fascia. 



Continuity with 
dartos fascia 


Continuity with superficial 
penile fascia 


Attachment to fascia lata 


Attachment to 
ischiopubic rami 


Superficial perineal 
fascia (Colles 1 fascia) 


External oblique muscle — 
and aponeurosis 


Membranous layer of 
superficial fascia 
(Scarpa's fascia) 


Fig. 4.26 Continuity of membranous layer of superficial fascia into other areas. 













































Abdomen 


sides of the penis to form the fundiform ligament of 
penis. In women, the membranous layer of the superficial 
fascia continues into the labia majora and the anterior part 
of the perineum. 

Anterolateral muscles 

There are five muscles in the anterolateral group of abdom¬ 
inal wall muscles: 

■ three flat muscles whose fibers begin posterolaterally, 
pass anteriorly, and are replaced by an aponeurosis as 
the muscle continues toward the midline—the external 
oblique, internal oblique, and transversus abdominis 
muscles; 

■ two vertical muscles, near the midline, which are 
enclosed within a tendinous sheath formed by the apo¬ 
neuroses of the flat muscles—the rectus abdominis and 
pyramidalis muscles. 

Each of these five muscles has specific actions, but 
together the muscles are critical for the maintenance of 


many normal physiological functions. By their positioning, 
they form a firm, but flexible, wall that keeps the abdominal 
viscera within the abdominal cavity, protects the viscera 
from injury, and helps maintain the position of the viscera 
in the erect posture against the action of gravity. 

In addition, contraction of these muscles assists in both 
quiet and forced expiration by pushing the viscera upward 
(which helps push the relaxed diaphragm further into the 
thoracic cavity) and in coughing and vomiting. 

All these muscles are also involved in any action that 
increases intraabdominal pressure, including parturition 
(childbirth), micturition (urination), and defecation (expul¬ 
sion of feces from the rectum). 

Flat muscles 

External oblique 

The most superficial of the three flat muscles in the antero¬ 
lateral group of abdominal wall muscles is the external 
oblique, which is immediately deep to the superficial 
fascia (Fig. 4.27, Table 4.1). Its laterally placed muscle 
fibers pass in an inferomedial direction, while its large 



Latissimus dorsi muscle 


Abdominal part of 
pectoralis major muscle 


Anterior superior iliac spine 


Aponeurosis of external oblique 


Inguinal ligament 


Linea alba 


External oblique muscle 


Fig. 4.27 External oblique muscle and its aponeurosis. 
















Regional anatomy • Abdominal Wall 


aponeurotic component covers the anterior part of the 
abdominal wall to the midline. Approaching the midline, 
the aponeuroses are entwined, forming the linea alba, 
which extends from the xiphoid process to the pubic 
symphysis. 

Associated ligaments 

The lower border of the external oblique aponeurosis forms 
the inguinal ligament on each side (Fig. 4.27). This 
thickened reinforced free edge of the external oblique apo¬ 
neurosis passes between the anterior superior iliac spine 
laterally and the pubic tubercle medially (Fig. 4.28). It folds 


under itself forming a trough, which plays an important 
role in the formation of the inguinal canal. 

Several other ligaments are also formed from extensions 
of the fibers at the medial end of the inguinal ligament: 

■ The lacunar ligament is a crescent-shaped extension 
of fibers at the medial end of the inguinal ligament that 
pass backward to attach to the pecten pubis on the 
superior ramus of the pubic bone (Figs. 4.28 and 4.29). 

■ Additional fibers extend from the lacunar ligament 
along the pecten pubis of the pelvic brim to form the 
pectineal (Cooper’s) ligament. 


Anterior superior 
iliac spine 


External oblique 

Aponeurosis of 
external oblique 



Inguinal ligament 


Lacunar ligament 


Femoral artery and vein 


Pubic tubercle 


Fig. 4.28 Ligaments formed from the external oblique 
aponeurosis. 



Fig. 4.29 Ligaments of the inguinal region. 



283 
























Abdomen 


Internal oblique 

Deep to the external oblique muscle is the internal 
oblique muscle, which is the second of the three flat 
muscles (Fig. 4.30, Table 4.1). This muscle is smaller and 
thinner than the external oblique, with most of its muscle 
fibers passing in a superomedial direction. Its lateral mus¬ 
cular components end anteriorly as an aponeurosis that 
blends into the linea alba at the midline. 


Transversus abdominis 

Deep to the internal oblique muscle is the transversus 
abdominis muscle (Fig. 4.31, Table 4.1), so named 
because of the direction of most of its muscle fibers. It ends 
in an anterior aponeurosis, which blends with the linea 
alba at the midline. 



Internal oblique muscle 
and aponeurosis 


External oblique muscle 


Rib X 


External oblique muscle 


Linea alba 


Aponeurosis of external oblique 


Fig. 4.30 Internal oblique muscle and its aponeurosis. 


284 





















Regional anatomy • Abdominal Wall 



External oblique muscle 
Rib X 


Transversus abdominis 
muscle and aponeurosis 


Anterior superior iliac spine 


External oblique muscle 


Aponeurosis of external oblique 


Aponeurosis of internal oblique 


Linea alba 


Fig. 4.31 Transversus abdominis muscle and its aponeurosis. 


Transversalis fascia 

Each of the three flat muscles is covered on its anterior and 
posterior surfaces by a layer of deep (or investing) fascia. 
In general, these layers are unremarkable except for the 
layer deep to the transversus abdominis muscle (the trans¬ 
versalis fascia), which is better developed. 

The transversalis fascia is a continuous layer of deep 
fascia that lines the abdominal cavity and continues into 
the pelvic cavity. It crosses the midline anteriorly, associat¬ 
ing with the transversalis fascia of the opposite side, and is 
continuous with the fascia on the inferior surface of the 
diaphragm. It is continuous posteriorly with the deep fascia 


covering the muscles of the posterior abdominal wall and 
attaches to the thoracolumbar fascia. 

After attaching to the crest of the ilium, the transversa¬ 
lis fascia blends with the fascia covering the muscles associ¬ 
ated with the upper regions of the pelvic bones and with 
similar fascia covering the muscles of the pelvic cavity. At 
this point, it is referred to as the parietal pelvic (or endo- 
pelvic) fascia. 

There is therefore a continuous layer of deep fascia sur¬ 
rounding the abdominal cavity that is thick in some areas, 
thin in others, attached or free, and participates in the 
formation of specialized structures. 


























286 


Abdomen 


Vertical muscles 

The two vertical muscles in the anterolateral group of 
abdominal wall muscles are the large rectus abdominis and 
the small pyramidalis (Fig. 4.32, Table 4.1). 


Rectus abdominis 

The rectus abdominis is a long, flat muscle and extends 
the length of the anterior abdominal wall. It is a paired 
muscle, separated in the midline by the linea alba, and it 


Table 4.1 Abdominal wall muscles 


Muscle 

Origin 

Insertion 

Innervation 

Function 

External oblique 

Muscular slips from the outer 
surfaces of the lower eight 
ribs (ribs V to XII) 

Lateral lip of iliac crest; 
aponeurosis ending in 
midline raphe (linea alba) 

Anterior rami of lower six 
thoracic spinal nerves 
(T7 to T12) 

Compress abdominal 
contents; both muscles flex 
trunk; each muscle bends 
trunk to same side, turning 
anterior part of abdomen to 
opposite side 

Internal oblique 

Thoracolumbar fascia; iliac 
crest between origins of 
external and transversus; 
lateral two-thirds of inguinal 
ligament 

Inferior border of the 
lower three or four ribs; 
aponeurosis ending in 
linea alba; pubic crest and 
pectineal line 

Anterior rami of lower six 
thoracic spinal nerves 
(T7 to T12) and LI 

Compress abdominal 
contents; both muscles flex 
trunk; each muscle bends 
trunk and turns anterior part 
of abdomen to same side 

Transversus 

abdominis 

Thoracolumbar fascia; medial 
lip of iliac crest; lateral 
one-third of inguinal 
ligament; costal cartilages 
lower six ribs (ribs VII to XII) 

Aponeurosis ending in 
linea alba; pubic crest and 
pectineal line 

Anterior rami of lower six 
thoracic spinal nerves 
(T7 to T12) and LI 

Compress abdominal 
contents 

Rectus abdominis 

Pubic crest, pubic tubercle, 
and pubic symphysis 

Costal cartilages of ribs V 
to VII; xiphoid process 

Anterior rami of lower 
seven thoracic spinal 
nerves (T7toT12) 

Compress abdominal 
contents; flex vertebral 
column; tense abdominal wall 

Pyramidalis 

Front of pubis and pubic 
symphysis 

Into linea alba 

Anterior ramus of T12 

Tenses the linea alba 


External oblique muscle 

Rectus abdominis muscle 

Tendinous intersection- 


Pyramidalis muscle 



Fig. 4.32 Rectus abdominis and pyramidalis muscles. 






























Regional anatomy • Abdominal Wall 



widens and thins as it ascends from the pubic symphysis to 
the costal margin. Along its course, it is intersected by 
three or four transverse fibrous bands or tendinous inter¬ 
sections (Fig. 4.32). These are easily visible on individuals 
with a well-developed rectus abdominis. 

Pyramidalis 

The second vertical muscle is the pyramidalis. This small, 
triangular muscle, which may be absent, is anterior to 
the rectus abdominis and has its base on the pubis, and its 
apex is attached superiorly and medially to the linea alba 
(Fig. 4.32). 

Rectus sheath 

The rectus abdominis and pyramidalis muscles are enclosed 
in an aponeurotic tendinous sheath (the rectus sheath) 
formed by a unique layering of the aponeuroses of the 
external and internal oblique, and transversus abdominis 
muscles (Fig. 4.33). 

The rectus sheath completely encloses the upper three- 
quarters of the rectus abdominis and covers the anterior 
surface of the lower one-quarter of the muscle. As no 
sheath covers the posterior surface of the lower quarter of 
the rectus abdominis muscle, the muscle at this point is in 
direct contact with the transversalis fascia. 


The formation of the rectus sheath surrounding the 
upper three-quarters of the rectus abdominis muscle has 
the following pattern: 

■ The anterior wall consists of the aponeurosis of the 
external oblique and half of the aponeurosis of the 
internal oblique, which splits at the lateral margin of 
the rectus abdominis. 

■ The posterior wall of the rectus sheath consists of the 
other half of the aponeurosis of the internal oblique 
and the aponeurosis of the transversus abdominis. 

At a point midway between the umbilicus and the pubic 
symphysis, corresponding to the beginning of the lower 
one-quarter of the rectus abdominis muscle, all of the apo¬ 
neuroses move anterior to the rectus muscle. There is no 
posterior wall of the rectus sheath and the anterior wall of 
the sheath consists of the aponeuroses of the external 
oblique, the internal oblique, and the transversus abdomi¬ 
nis muscles. From this point inferiorly, the rectus abdomi¬ 
nis muscle is in direct contact with the transversalis fascia. 
Marking this point of transition is an arch of fibers (the 
arcuate line; see Fig. 4.32). 


Linea alba Rectus abdominis 

External oblique 



Linea alba Rectus abdominis 

External oblique 



Fig. 4.33 Organization of the rectus sheath. A. Transverse section through the upper three-quarters of the rectus sheath. B. Transverse 
section through the lower one-quarter of the rectus sheath. 


287 






















Abdomen 


Extraperitoneal fascia 

Deep to the transversalis fascia is a layer of connective 
tissue, the extraperitoneal fascia, which separates the 
transversalis fascia from the peritoneum (Fig. 4.34). Con¬ 
taining varying amounts of fat, this layer not only lines the 
abdominal cavity but is also continuous with a similar 
layer lining the pelvic cavity. It is abundant on the posterior 
abdominal wall, especially around the kidneys, continues 
over organs covered by peritoneal reflections, and, as the 
vasculature is located in this layer, extends into mesenter¬ 
ies with the blood vessels. Viscera in the extraperitoneal 
fascia are referred to as retroperitoneal. 

In the description of specific surgical procedures, the 
terminology used to describe the extraperitoneal fascia is 
further modified. The fascia toward the anterior side of the 
body is described as preperitoneal (or, less commonly, pro- 
peritoneal) and the fascia toward the posterior side of the 
body has been described as retroperitoneal (Fig. 4.35). 


Examples of the use of these terms would be the continuity 
of fat in the inguinal canal with the preperitoneal fat and 
a transabdominal preperitoneal laparoscopic repair of an 
inguinal hernia. 

Peritoneum 

Deep to the extraperitoneal fascia is the peritoneum (see 
Figs. 4.6 and 4.7 on pp. 260-261). This thin serous mem¬ 
brane lines the walls of the abdominal cavity and, at 
various points, reflects onto the abdominal viscera, provid¬ 
ing either a complete or a partial covering. The peritoneum 
lining the walls is the parietal peritoneum; the peritoneum 
covering the viscera is the visceral peritoneum. 

The continuous lining of the abdominal walls by the 
parietal peritoneum forms a sac. This sac is closed in men 
but has two openings in women where the uterine tubes 
provide a passage to the outside. The closed sac in men and 
the semiclosed sac in women is called the peritoneal cavity. 


Superficial fascia 


Fatty layer Membranous layer 
(Camper's) (Scarpa's) 



External oblique muscle 
Internal oblique muscle 

Transversus abdominis muscle 


Aponeuroses 


Transversalis fascia 
Extraperitoneal fascia 
Parietal peritoneum 

Visceral peritoneum 


Fig. 4.34 Transverse section showing the layers of the abdominal wall. 


























Regional anatomy • Abdominal Wall 



Extraperitoneal fascia 


Preperitoneal Retroperitoneal 



Innervation 

The skin, muscles, and parietal peritoneum of the antero¬ 
lateral abdominal wall are supplied by T7 to T12 and LI 
spinal nerves. The anterior rami of these spinal nerves pass 
around the body, from posterior to anterior, in an infero- 
medial direction (Fig. 4.36). As they proceed, they give off 
a lateral cutaneous branch and end as an anterior cutane¬ 
ous branch. 

The intercostal nerves (T7 to T11) leave their intercostal 
spaces, passing deep to the costal cartilages, and continue 
onto the anterolateral abdominal wall between the inter¬ 
nal oblique and transversus abdominis muscles (Fig. 4.37). 
Reaching the lateral edge of the rectus sheath, they enter 
the rectus sheath and pass posterior to the lateral aspect 
of the rectus abdominis muscle. Approaching the midline, 
an anterior cutaneous branch passes through the rectus 
abdominis muscle and the anterior wall of the rectus 
sheath to supply the skin. 


Xiphoid process 


Lateral cutaneous- 

branches T7 to T12 


External oblique muscle — 
and aponeurosis 

Iliohypogastric nerve (LI)- 


llio-inguinal nerve (LI) 



-Iliac crest 


Anterior cutaneous 
branches T7 to T12 


Fig. 4.36 Innervation of the anterolateral abdominal wall. 


289 


























Abdomen 



Rectus abdominis muscle 


Transversus abdominis muscle 


Linea alba 


T12 nerve 

Iliohypogastric nerve (LI) 
llio-inguinal nerve (LI) 


T10 nerve 


Fig. 4.37 Path taken by the nerves innervating the anterolateral abdominal wall. 


Spinal nerve T12 (the subcostal nerve) follows a 
similar course as the intercostals. Branches of LI (the ilio¬ 
hypogastric nerve and ilio-inguinal nerve), which 
originate from the lumbar plexus, follow similar courses 
initially, but deviate from this pattern near their final 
destination. 

Along their course, nerves T7 to T12 and LI supply 
branches to the anterolateral abdominal wall muscles 
and the underlying parietal peritoneum. All terminate by 
supplying skin: 

■ Nerves T7 to T9 supply the skin from the xiphoid process 
to just above the umbilicus. 

■ T10 supplies the skin around the umbilicus. 

■ Til, T12, and LI supply the skin from just below 
the umbilicus to, and including, the pubic region 
(Fig. 4.38). 

■ Additionally, the ilio-inguinal nerve (a branch of 
LI) supplies the anterior surface of the scrotum or 
labia majora, and sends a small cutaneous branch to 
the thigh. 



Fig. 4.38 Dermatomes of the anterolateral abdominal wall. 


290 


































Regional anatomy • Abdominal Wall 



Arterial supply and venous drainage 

Numerous blood vessels supply the anterolateral abdomi¬ 
nal wall. Superficially: 

■ the superior part of the wall is supplied by branches 
from the musculophrenic artery, a terminal branch 
of the internal thoracic artery, and 

■ the inferior part of the wall is supplied by the medially 
placed superficial epigastric artery and the laterally 
placed superficial circumflex iliac artery, both 
branches of the femoral artery (Fig. 4.39). 


At a deeper level: 

■ the superior part of the wall is supplied by the superior 
epigastric artery, a terminal branch of the internal 
thoracic artery; 

■ the lateral part of the wall is supplied by branches of the 

tenth and eleventh intercostal arteries and the 
subcostal artery; and 

■ the inferior part of the wall is supplied by the medially 
placed inferior epigastric artery and the laterally 
placed deep circumflex iliac artery, both branches of 
the external iliac artery. 



Superficial circumflex 
iliac artery 


Internal thoracic artery 


Superior epigastric artery 


Intercostal arteries 


Musculophrenic artery 


Inferior epigastric artery 


Deep circumflex 
iliac artery 


Superficial epigastric artery 


Fig. 4.39 Arterial supply to the anterolateral abdominal wall. 


291 























Abdomen 


The superior and inferior epigastric arteries both enter 
the rectus sheath. They are posterior to the rectus abdomi¬ 
nis muscle throughout their course, and anastomose with 
each other (Fig. 4.40). 

Veins of similar names follow the arteries and are 
responsible for venous drainage. 

Lymphatic drainage 

Lymphatic drainage of the anterolateral abdominal wall 
follows the basic principles of lymphatic drainage: 

■ Superficial lymphatics above the umbilicus pass in a 
superior direction to the axillary nodes, while drain¬ 
age below the umbilicus passes in an inferior direction 

to the superficial inguinal nodes. 


Deep lymphatic drainage follows the deep arteries back 
to parasternal nodes along the internal thoracic 
artery, lumbar nodes along the abdominal aorta, and 
external iliac nodes along the external iliac artery. 


GROIN 

The groin (inguinal region) is the area of junction between 
the anterior abdominal wall and the thigh. In this area, the 
abdominal wall is weakened from changes that occur 
during development and a peritoneal sac or diverticulum, 
with or without abdominal contents, can therefore pro¬ 
trude through it, creating an inguinal hernia. This type 
of hernia can occur in both sexes, but it is most common 
in males. 



Rectus abdominis muscle 


Transversus abdominis muscle 


Internal thoracic artery 

Superior epigastric artery 


Musculophrenic artery 


Inferior epigastric artery 
Deep circumflex iliac artery 


Fig. 4.40 Superior and inferior epigastric arteries. 





















Regional anatomy • Groin 



The inherent weakness in the anterior abdominal wall 
in the groin is caused by changes that occur during the 
development of the gonads. Before the descent of the testes 
and ovaries from their initial position high in the posterior 
abdominal wall, a peritoneal outpouching (the processus 
vaginalis) forms (Fig. 4.41), protruding through the 
various layers of the anterior abdominal wall and acquir¬ 
ing coverings from each: 

■ The transversalis fascia forms its deepest covering. 

■ The second covering is formed by the musculature of 
the internal oblique (a covering from the transversus 
abdominis muscle is not acquired because the processus 
vaginalis passes under the arching fibers of this abdomi¬ 
nal wall muscle). 

■ Its most superficial covering is the aponeurosis of the 
external oblique. 


As a result the processus vaginalis is transformed into a 
tubular structure with multiple coverings from the layers 
of the anterior abdominal wall. This forms the basic struc¬ 
ture of the inguinal canal. 

The final event in this development is the descent of 
the testes into the scrotum or of the ovaries into the 
pelvic cavity. This process depends on the development 
of the gubernaculum, which extends from the inferior 
border of the developing gonad to the labioscrotal swellings 
(Fig. 4.41). 

The processus vaginalis is immediately anterior to the 
gubernaculum within the inguinal canal. 

In men, as the testes descend, the testes and their 
accompanying vessels, ducts, and nerves pass through the 
inguinal canal and are therefore surrounded by the same 
fascial layers of the abdominal wall. Testicular descent 
completes the formation of the spermatic cord in men. 


Parietal peritoneum Extraperitoneal fascia 

Transversalis fascia 

Transversus abdominis muscle 


Internal oblique muscle 


External oblique muscle 


Processus vaginalis 



Fig. 4.41 Descent of the testis from week 7 (postfertilization) to birth. 


293 

















Abdomen 


In women, the ovaries descend into the pelvic cavity and 
become associated with the developing uterus. Therefore, 
the only remaining structure passing through the inguinal 
canal is the round ligament of the uterus, which is a 
remnant of the gubernaculum. 

The development sequence is concluded in both sexes 
when the processus vaginalis obliterates. If this does not 
occur or is incomplete, a potential weakness exists in the 
anterior abdominal wall and an inguinal hernia may 
develop. In males, only proximal regions of the tunica vagi¬ 
nalis obliterate. The distal end expands to enclose most of 
the testis in the scrotum. In other words, the cavity of the 
tunica vaginalis in men forms as an extension of the devel¬ 
oping peritoneal cavity that becomes separated off during 
development. 

Inguinal canal 

The inguinal canal is a slit-like passage that extends in a 
downward and medial direction, just above and parallel to 
the lower half of the inguinal ligament. It begins at the 


deep inguinal ring and continues for approximately 4 cm, 
ending at the superficial inguinal ring (Fig. 4.42). The con¬ 
tents of the canal are the genital branch of the genitofemo¬ 
ral nerve, the spermatic cord in men, and the round 
ligament of the uterus in women. Additionally, in both 
sexes, the ilio-inguinal nerve passes through part of the 
canal, exiting through the superficial inguinal ring with 
the other contents. 

Deep inguinal ring 

The deep (internal) inguinal ring is the beginning of the 
inguinal canal and is at a point midway between the ante¬ 
rior superior iliac spine and the pubic symphysis (Fig. 
4.43). It is just above the inguinal ligament and immedi¬ 
ately lateral to the inferior epigastric vessels. Although 
sometimes referred to as a defect or opening in the trans¬ 
versals fascia, it is actually the beginning of the tubular 
evagination of transversalis fascia that forms one of the 
coverings (the internal spermatic fascia) of the sper¬ 
matic cord in men or the round ligament of the uterus in 
women. 



Superficial 
inguinal ring 


Spermatic cord 


Linea alba 


Anterior superior 
iliac spine 


Deep inguinal ring 


External oblique muscle 
Aponeurosis of external oblique 

Inguinal ligament 


Fig. 4.42 Inguinal canal. 


294 

















Regional anatomy • Groin 


Transversalis fascia 



Superficial inguinal ring 

The superficial (external) inguinal ring is the end of the 
inguinal canal and is superior to the pubic tubercle (Fig. 
4.44). It is a triangular opening in the aponeurosis of the 
external oblique, with its apex pointing superolaterally and 
its base formed by the pubic crest. The two remaining sides 
of the triangle (the medial crus and the lateral crus) are 
attached to the pubic symphysis and the pubic tubercle, 
respectively. At the apex of the triangle the two crura are 
held together by crossing (intercrural) fibers, which prevent 
further widening of the superficial ring. 

As with the deep inguinal ring, the superficial inguinal 
ring is actually the beginning of the tubular evagination 
of the aponeurosis of the external oblique onto the struc¬ 
tures traversing the inguinal canal and emerging from the 
superficial inguinal ring. This continuation of tissue over 
the spermatic cord is the external spermatic fascia. 


External oblique muscle 
Anterior superior iliac spine 

Inguinal ligament 



Femoral artery and vein 


Aponeurosis of external oblique 

Superficial inguinal ring 
Spermatic cord 


Fig. 4.44 Superficial inguinal ring and the aponeurosis of the external oblique. 






























Abdomen 


Anterior wall 

The anterior wall of the inguinal canal is formed along its 
entire length by the aponeurosis of the external oblique 
muscle (Fig. 4.44). It is also reinforced laterally by the 
lower fibers of the internal oblique that originate from the 
lateral two-thirds of the inguinal ligament (Fig. 4.45). This 
adds an additional covering over the deep inguinal ring, 
which is a potential point of weakness in the anterior 
abdominal wall. Furthermore, as the internal oblique 
muscle covers the deep inguinal ring, it also contributes a 
layer (the cremasteric fascia containing the cremas¬ 
teric muscle) to the coverings of the structures traversing 
the inguinal canal. 

Posterior wall 

The posterior wall of the inguinal canal is formed along its 
entire length by the transversalis fascia (see Fig. 4.43). It is 
reinforced along its medial one-third by the conjoint 
tendon (inguinal falx; Fig. 4.45). This tendon is the com¬ 
bined insertion of the transversus abdominis and internal 
oblique muscles into the pubic crest and pectineal line. 

As with the internal oblique muscle’s reinforcement of 
the area of the deep inguinal ring, the position of the con¬ 
joint tendon posterior to the superficial inguinal ring 


provides additional support to a potential point of weak¬ 
ness in the anterior abdominal wall. 

Roof 

The roof (superior wall) of the inguinal canal is formed by 
the arching fibers of the transversus abdominis and inter¬ 
nal oblique muscles (Figs. 4.45 and 4.46). They pass from 
their lateral points of origin from the inguinal ligament to 
their common medial attachment as the conjoint tendon. 

Floor 

The floor (inferior wall) of the inguinal canal is formed by 
the medial one-half of the inguinal ligament. This rolled- 
under, free margin of the lowest part of the aponeurosis of 
the external oblique forms a gutter or trough on which the 
contents of the inguinal canal are positioned. The lacunar 
ligament reinforces most of the medial part of the gutter. 

Contents 

The contents of the inguinal canal are: 

■ the spermatic cord in men, and 

■ the round ligament of the uterus and genital branch of 
the genitofemoral nerve in women. 


Internal oblique muscle 
Anterior superior iliac spine 


Inguinal ligament 


Femoral artery and vein 



Aponeurosis of internal oblique 


Conjoint tendon 
Spermatic cord 


Fig. 4.45 Internal oblique muscle and the inguinal canal. 


296 














Regional anatomy • Groin 


Transversus abdominis muscle 



These structures enter the inguinal canal through the 
deep inguinal ring and exit it through the superficial ingui¬ 
nal ring. 

Additionally, the ilio-inguinalnerve (LI) passes through 
part of the inguinal canal. This nerve is a branch of the 
lumbar plexus, enters the abdominal wall posteriorly by 
piercing the internal surface of the transversus abdominis 
muscle, and continues through the layers of the anterior 
abdominal wall by piercing the internal oblique muscle. As 
it continues to pass inferomedially, it enters the inguinal 
canal. It continues down the canal to exit through the 
superficial inguinal ring. 

Spermatic cord 

The spermatic cord begins to form proximally at the deep 
inguinal ring and consists of structures passing between 
the abdominopelvic cavities and the testis, and the three 
fascial coverings that enclose these structures (Fig. 4.47). 
The structures in the spermatic cord include: 

■ the ductus deferens, 

■ the artery to the ductus deferens (from the inferior 
vesical artery), 


■ the testicular artery (from the abdominal aorta), 

■ the pampiniform plexus of veins (testicular veins), 

■ the cremasteric artery and vein (small vessels associated 
with the cremasteric fascia), 

■ the genital branch of the genitofemoral nerve (innerva¬ 
tion to the cremasteric muscle), 

■ sympathetic and visceral afferent nerve fibers, 

■ lymphatics, and 

■ remnants of the processus vaginalis. 

These structures enter the deep inguinal ring, proceed 
down the inguinal canal, and exit from the superficial 
inguinal ring, having acquired the three fascial coverings 
during their journey. This collection of structures and 
fascias continues into the scrotum where the structures 
connect with the testes and the fascias surround the testes. 

Three fascias enclose the contents of the spermatic 
cord: 

■ The internal spermatic fascia, which is the deepest layer, 
arises from the transversalis fascia and is attached to the 
margins of the deep inguinal ring. 

■ The cremasteric fascia with the associated cremasteric 
muscle, which is the middle fascial layer, arises from the 
internal oblique muscle. 

■ The external spermatic fascia, which is the most super¬ 
ficial covering of the spermatic cord, arises from the 
aponeurosis of the external oblique muscle and is 
attached to the margins of the superficial inguinal ring 
(Fig. 4.47). 

Round ligament of the uterus 

The round ligament of the uterus is a cord-like structure 
that passes from the uterus to the deep inguinal ring where 
it enters the inguinal canal. It passes down the inguinal 
canal and exits through the superficial inguinal ring. At 
this point, it has changed from a cord-like structure to a 
few strands of tissue, which attach to the connective tissue 
associated with the labia majora. As it traverses the ingui¬ 
nal canal, it acquires the same coverings as the spermatic 
cord in men. 

The round ligament of the uterus is the long distal part 
of the original gubernaculum in the fetus that extends 
from the ovary to the labioscrotal swellings. From its 
attachment to the uterus, the round ligament of the 
uterus continues to the ovary as the ligament of the 
ovary that develops from the short proximal end of 
the gubernaculum. 















Abdomen 



Genital branch of genitofemoral nerve 


Cremasteric vessels 

Ductus deferens 
Artery to ductus deferens 


Testicular artery and 
pampiniform plexus of veins 

Parietal peritoneum 

Extraperitoneal fascia 

Transversalis fascia 


Conjoint tendon 


External oblique 
aponeurosis 


Transversus abdominis muscle 
Deep inguinal ring 
Superficial inguinal ring 

External spermatic fascia 
Cremasteric fascia 
Internal spermatic fascia 

Parietal layer of the tunica vaginalis 
Cavity of the tunica vaginalis 
Visceral layer of the tunica vaginalis 


External oblique 
aponeurosis 


Internal oblique muscle 


Fig. 4.47 Spermatic cord. 








































Regional anatomy • Groin 


In the clinic 
Cremasteric reflex 

In men, the cremaster muscle and cremasteric fascia 
form the middle or second covering of the spermatic 
cord. This muscle and its associated fascia are supplied 
by the genital branch of the genitofemoral nerve (LI/ 
L2). Contraction of this muscle and the resulting 
elevation of the testis can be stimulated by a reflex arc. 
Gently touching the skin at and around the anterior 
aspect of the superior part of the thigh stimulates the 
sensory fibers in the ilio-inguinal nerve. These sensory 
fibers enter the spinal cord at level LI. At this level, the 
sensory fibers stimulate the motor fibers carried in the 
genital branch of the genitofemoral nerve, which results 
in contraction of the cremaster muscle and elevation of 
the testis. 

The cremasteric reflex is more active in children, 
tending to diminish with age. As with many reflexes, it 
may be absent in certain neurological disorders. 
Although it can be used for testing spinal cord function 
at level LI in men, its clinical use is limited. 


Inferior epigastric vessels 



Conjoint tendon 


Superficial inguinal ring 


Peritoneal sac 


Testis 


Extraperitoneal fascia 
Parietal peritoneum 


Deep inguinal ring 


Fig. 4.48 Indirect inguinal hernia. 


Inguinal hernias 

An inguinal hernia is the protrusion or passage of a peri¬ 
toneal sac, with or without abdominal contents, through 
a weakened part of the abdominal wall in the groin. It 
occurs because the peritoneal sac enters the inguinal 
canal either: 

■ indirectly, through the deep inguinal ring, or 

■ directly, through the posterior wall of the inguinal 
canal. 

Inguinal hernias are therefore classified as either indi¬ 
rect or direct. 

Indirect inguinal hernias 

The indirect inguinal hernia is the most common of the 
two types of inguinal hernia and is much more common 
in men than in women (Fig. 4.48). It occurs because some 


part, or all, of the embryonic processus vaginalis remains 
open or patent. It is therefore referred to as being congeni¬ 
tal in origin. 

The protruding peritoneal sac enters the inguinal canal 
by passing through the deep inguinal ring, just lateral to 
the inferior epigastric vessels. The extent of its excursion 
down the inguinal canal depends on the amount of proces¬ 
sus vaginalis that remains patent. If the entire processus 
vaginalis remains patent, the peritoneal sac may traverse 
the length of the canal, exit the superficial inguinal ring, 
and continue into the scrotum in men or the labia majus 
in women. In this case, the protruding peritoneal sac 
acquires the same three coverings as those associated with 
the spermatic cord in men or the round ligament of the 
uterus in women. 














Abdomen 


Direct inguinal hernias 

A peritoneal sac that enters the medial end of the inguinal 
canal directly through a weakened posterior wall is a direct 
inguinal hernia (Fig. 4.49). It is usually described as 
acquired because it develops when abdominal musculature 
has been weakened, and is commonly seen in mature men. 
The bulging occurs medial to the inferior epigastric vessels 
in the inguinal triangle (Hesselbach’s triangle), which is 
bounded: 

■ laterally by the inferior epigastric artery, 

■ medially by the rectus abdominis muscle, and 

■ interiorly by the inguinal ligament (Fig. 4.50). 

Internally, a thickening of the transversalis fascia (the 
iliopubic tract) follows the course of the inguinal ligament 
(Fig. 4.50). 

This type of inguinal hernia does not traverse the entire 
length of the inguinal canal but may exit through the 
superficial inguinal ring. When this occurs, the peritoneal 
sac acquires a layer of external spermatic fascia and can 
extend, like an indirect hernia, into the scrotum. 


Inferior epigastric vessels 




Deep inguinal ring 

Transversus abdominis muscle 

Anterior superior iliac spine 

Iliopubic tract 

Testicular vessels 

External iliac artery 

External iliac vein 

Ductus deferens 


Rectus abdominis muscle 

Inguinal triangle 

Superficial inguinal ring 

Lacunar ligament 
A 


Inferior epigastric vessels 


300 


Fig. 4.50 Right inguinal triangle. A. Internal view. 
























Regional anatomy • Groin 


Direct hernia — 


Medial 









4 / jjj 


B 


• 

* 


- Inferior epigastric 
vessels 


Lateral 

- Position of deep 
inguinal ring 


— Testicular vessels 


Ductus deferens External iliac vessels 

Fig. 4.50, cont’d B. Laparoscopic view showing the parietal peritoneum still covering the area. 


In the clinic 

Masses around the groin 

Around the groin there is a complex confluence of 
anatomical structures. Careful examination and good 
anatomical knowledge allows determination of the 
correct anatomical structure from which the mass arises 
and therefore the diagnosis. The most common masses in 
the groin are hernias. 

The key to groin examination is determining the 
position of the inguinal ligament. The inguinal ligament 
passes between the anterior superior iliac spine laterally 
and the pubic tubercle medially. Inguinal hernias are 
above the inguinal ligament and are usually more 
apparent on standing. A visual assessment of the lump is 
necessary, bearing in mind the anatomical landmarks of 
the inguinal ligament. 

In men, it is wise to examine the scrotum to check for a 
lump. If an abnormal mass is present, an inability to feel 
its upper edge suggests that it may originate from the 
inguinal canal and might be a hernia. By placing the hand 
over the lump and asking the patient to cough, the lump 
bulges outward. 

An attempt should be made to reduce the swelling by 
applying gentle, firm pressure over the lump. If the lump 
is reducible, the hand should be withdrawn and careful 
observation will reveal recurrence of the mass. 

The position of an abnormal mass in the groin relative 
to the pubic tubercle is very important, as are the 
presence of increased temperature and pain, which may 
represent early signs of strangulation or infection. 

As a general rule: 

■ An inguinal hernia appears through the superficial 
inguinal ring above the pubic tubercle and crest. 


■ A femoral hernia (see below) appears through the 
femoral canal below and lateral to the pubic 
tubercle. 

A hernia is the protrusion of a viscus, in part or in 
whole, through a normal or abnormal opening. The viscus 
usually carries a covering of parietal peritoneum, which 
forms the lining of the hernial sac. 

Inguinal hernias 

Hernias occur in a variety of regions. The commonest 
site is the groin of the lower anterior abdominal wall. In 
some patients, inguinal hernias are present from birth 
(congenital) and are caused by the persistence of the 
processus vaginalis and the passage of viscera through 
the inguinal canal. Acquired hernias occur in older 
patients and causes include raised intraabdominal 
pressure (e.g., from repeated coughing associated with 
lung disease), damage to nerves of the anterior abdominal 
wall (e.g., from surgical abdominal incisions), and 
weakening of the walls of the inguinal canal. 

One of the potential problems with hernias is that 
bowel and fat may become stuck within the hernial sac. 
This can cause appreciable pain and bowel obstruction, 
necessitating urgent surgery. Another potential risk is 
strangulation of the hernia, in which the blood supply 
to the bowel is cut off at the neck of the hernial sac, 
rendering the bowel ischemic and susceptible to 
perforation. 

The hernial sac of an indirect inguinal hernia enters 
the deep inguinal ring and passes through the inguinal 
canal. If the hernia is large enough, the hernial sac may 

(continues) 



Abdomen 


In the clinic—cont'd 

emerge through the superficial inguinal ring. In men, such 
a hernia may extend into the scrotum (Fig. 4.51). 

The hernial sac of a direct inguinal hernia pushes 
forward through the posterior wall of the inguinal canal 
immediately posterior to the superficial inguinal ring. 

The hernia protrudes directly forward medial to the 
inferior epigastric vessels and through the superficial 
inguinal ring. 

The differentiation between an indirect and a direct 
inguinal hernia is made during surgery when the inferior 
epigastric vessels are identified at the medial edge of the 
deep internal ring: 

■ An indirect hernial sac passes lateral to the inferior 
epigastric vessels. 

■ A direct hernia is medial to the inferior epigastric 
vessels. 

Inguinal hernias occur more commonly in men than in 
women possibly because men have a much larger 
inguinal canal than women. 

Femoral hernias 

A femoral hernia passes through the femoral canal and 
into the medial aspect of the anterior thigh. The femoral 


Right indirect Corpus spongiosum 

inguinal hernia Corpora cavernosa 



Right testis — 1 1 —Left testis 

Fig. 4.51 Right indirect inguinal hernia. T2, fat saturated, 
weighted magnetic resonance image in the coronal plane of 
a male groin. 


canal lies at the medial edge of the femoral sheath, which 
contains the femoral artery, femoral vein, and lymphatics. 
The neck of the femoral canal is extremely narrow and is 
prone to trapping bowel within the sac, so making this 
type of hernia irreducible and susceptible to bowel 
strangulation. Femoral hernias are usually acquired, are 
not congenital, and most commonly occur in middle-aged 
and elderly populations. In addition, because women 
generally have wider pelvises than men, they tend to 
occur more commonly in women. 

Sportsmen's groin/sportsmen's hernia 
The groin can loosely be defined as the area where the leg 
meets the trunk near the midline. Here the abdominal 
muscles of the trunk blend in with the adductor muscles 
of the thigh, the medial end of the inguinal ligament 
attaches to the pubic tubercle, the pubic symphysis 
attaches the two pubic bones together, and the superficial 
(external) inguinal ring occurs. It also is in and around this 
region where there is considerable translation of force 
during most athletic and sporting activities. Pain in the 
groin or pubic region can be due to numerous causes, 
which include inflammatory changes at the pubic 
symphysis, insertional problems of the rectus abdominis/ 
adductor longus, and hernias. 

Umbilical hernias 

Umbilical hernias are rare. Occasionally, they are 
congenital and result from failure of the small bowel to 
return to the abdominal cavity from the umbilical cord 
during development. After birth, umbilical hernias may 
result from incomplete closure of the umbilicus (navel). 
Overall, most of these hernias close in the first year of life, 
and surgical repair is not generally attempted until later. 

Para-umbilical hernias may occur in adults at and 
around the umbilicus and often have small necks, so 
requiring surgical treatment. 

Incisional hernias 

Incisional hernias occur through a defect in a scar of a 
previous abdominal operation. Usually, the necks of these 
hernias are wide and do not therefore strangulate the 
viscera they contain. 

Other hernias 

A spigelian hernia passes upward through the arcuate 
line into the lateral border at the lower part of the 
posterior rectus sheath. It may appear as a tender mass on 
one side of the lower anterior abdominal wall. 

Abdominopelvic cavity hernias can also develop in 
association with the pelvic walls, and sites include the 
obturator canal, the greater sciatic foramen and above 
and below the piriformis muscle. 


302 







Regional anatomy • Abdominal Viscera 


ABDOMINAL VISCERA 
Peritoneum 

A thin membrane (the peritoneum) lines the walls of the 
abdominal cavity and covers much of the viscera. The pari¬ 
etal peritoneum lines the walls of the cavity and the vis¬ 
ceral peritoneum covers the viscera. Between the parietal 
and visceral layers of peritoneum is a potential space 
(the peritoneal cavity). Abdominal viscera either are sus¬ 
pended in the peritoneal cavity by folds of peritoneum 
(mesenteries) or are outside the peritoneal cavity. Organs 
suspended in the cavity are referred to as intraperitoneal 
(Fig. 4.52); organs outside the peritoneal cavity, with only 
one surface or part of one surface covered by peritoneum, 
are retroperitoneal. 

Innervation of the peritoneum 

The parietal peritoneum associated with the abdominal 
wall is innervated by somatic afferents carried in branches 
of the associated spinal nerves and is therefore sensitive to 
well-localized pain. The visceral peritoneum is innervated 
by visceral afferents that accompany autonomic nerves 
(sympathetic and parasympathetic) back to the central 
nervous system. Activation of these fibers can lead to 
referred and poorly localized sensations of discomfort, and 
to reflex visceral motor activity. 


-Visceral peritoneum 


Mesentery 



Fig. 4.52 A. Intraperitoneal. B. Retroperitoneal. 












Abdomen 


Peritoneal cavity 

The peritoneal cavity is subdivided into the greater sac and 

the omental bursa (lesser sac; Fig. 4.53). 

■ The greater sac accounts for most of the space in 
the peritoneal cavity, beginning superiorly at the dia¬ 
phragm and continuing interiorly into the pelvic cavity. 
It is entered once the parietal peritoneum has been 
penetrated. 

■ The omental bursa is a smaller subdivision of the peri¬ 
toneal cavity posterior to the stomach and liver and is 


continuous with the greater sac through an opening, 
the omental (epiploic) foramen (Fig. 4.54). 

Surrounding the omental (epiploic) foramen are numer¬ 
ous structures covered with peritoneum. They include the 
portal vein, hepatic artery proper, and bile duct anteriorly; 
the inferior vena cava posteriorly; the caudate lobe of 
the liver superiorly; and the first part of the duodenum 
inferiorly. 


Diaphragm 


Liver 

Lesser omentum 

Stomach 
Transverse mesocolon 

Transverse colon 
Greater sac 

Greater omentum 


Small intestine 



— Omental bursa 
Pancreas 


Duodenum 


Mesentery 


Fig. 4.53 Greater and lesser sacs of the peritoneal cavity. 


304 



































Regional anatomy • Abdominal Viscera 


Falciform ligament 



Hepatic artery proper 


Lesser omentum 


Bile duct 


Gastric vessels 


Portal vein 


Stomach 


Omental 

bursa 


Spleen 


Left kidney 


Liver 


Omental 

foramen 


Greater sac— 


Right kidney 


I nf erior vena cava TX11 


Aorta 


Fig. 4.54 Transverse section illustrating the continuity between the greater and lesser sacs through the omental (epiploic) foramen. 


In the clinic 

Peritoneum 

A small volume of peritoneal fluid within the peritoneal 
cavity lubricates movement of the viscera suspended in 
the abdominal cavity. 

The peritoneal space has a large surface area, which 
facilitates the spread of disease through the peritoneal 
cavity and over the bowel and visceral surfaces. 
Conversely, this large surface area can be used for 
administering certain types of treatment and a 
number of procedures. 

Ventriculoperitoneal shunts 

Patients with obstructive hydrocephalus (an excessive 
accumulation of cerebrospinal fluid within the cerebral 
ventricular system) require continuous drainage of this 
fluid. This is achieved by placing a fine-bore catheter 
through the skull into the cerebral ventricles and placing 
the extracranial part of the tube beneath the scalp and 


skin of the chest wall and then passing it through the 
abdominal wall into the peritoneal cavity. Cerebrospinal 
fluid drains through the tube into the peritoneal cavity, 
where it is absorbed. 

Dialysis and peritoneal dialysis 

People who develop renal failure require dialysis to live. 
There are two methods. 

In the first method (hemodialysis), blood is taken from 
the circulation, dialyzed through a complex artificial 
membrane, and returned to the body. A high rate of 
blood flow is required to remove excess body fluid, 
exchange electrolytes, and remove noxious metabolites. 
To accomplish this, either an arteriovenous fistula is 
established surgically (by connecting an artery to a vein, 
usually in the upper limb, and requiring approximately six 
weeks to "mature") and is cannulated each time the 
patient returns for dialysis, or a large-bore cannula is 

(continues) 


























Abdomen 


In the clinic—cont'd 

placed into the right atrium, through which blood can be 
aspirated and returned. 

In the second method of dialysis, the peritoneum is 
used as the dialysis membrane. The large surface area of 
the peritoneal cavity is an ideal dialysis membrane for 
fluid and electrolyte exchange. To accomplish dialysis, a 
small tube is inserted through the abdominal wall and 
dialysis fluid is injected into the peritoneal cavity. 
Electrolytes and molecules are exchanged across the 
peritoneum between the fluid and blood. Once dialysis is 
completed, the fluid is drained. 

Peritoneal spread of disease 

The large surface area of the peritoneal cavity allows 
infection and malignant disease to spread easily 
throughout the abdomen (Fig. 4.55). If malignant cells 
enter the peritoneal cavity by direct invasion (e.g., from 
colon or ovarian cancer), spread may be rapid. Similarly, a 
surgeon excising a malignant tumor and releasing 
malignant cells into the peritoneal cavity may cause an 
appreciable worsening of the patient's prognosis. 

Infection can also spread across the large surface area. 

The peritoneal cavity can also act as a barrier to, and 
container of, disease. Intraabdominal infection therefore 
tends to remain below the diaphragm rather than spread 
into other body cavities. 

Perforated bowel 

A perforated bowel (e.g., caused by a perforated duodenal 
ulcer) often leads to the release of gas into the peritoneal 


cavity. This peritoneal gas can be easily visualized on an 
erect chest radiograph—gas can be demonstrated in 
extremely small amounts beneath the diaphragm. A 
patient with severe abdominal pain and subdiaphragmatic 
gas needs a laparotomy. 



Fig. 4.55 Peritoneal metastasis on the surface of the liver. 
Computed tomogram in the axial plane of the upper abdomen. 


306 









Regional anatomy • Abdominal Viscera 


Omenta, mesenteries, and ligaments 

Throughout the peritoneal cavity numerous peritoneal 
folds connect organs to each other or to the abdominal 
wall. These folds (omenta, mesenteries, and ligaments) 
develop from the original dorsal and ventral mesenteries, 
which suspend the developing gastrointestinal tract in the 
embryonic coelomic cavity Some contain vessels and 
nerves supplying the viscera, while others help maintain 
the proper positioning of the viscera. 

Omenta 

The omenta consist of two layers of peritoneum, which 
pass from the stomach and the first part of the duodenum 
to other viscera. There are two: 

■ the greater omentum, derived from the dorsal mesen¬ 
tery, and 

■ the lesser omentum, derived from the ventral 
mesentery. 

Greater omentum 

The greater omentum is a large, apron-like, peritoneal 
fold that attaches to the greater curvature of the stomach 
and the first part of the duodenum (Fig. 4.56). It drapes 
inferiorly over the transverse colon and the coils of the 
jejunum and ileum (see Fig. 4.53). Turning posteriorly, it 
ascends to associate with, and become adherent to, the 
peritoneum on the superior surface of the transverse colon 
and the anterior layer of the transverse mesocolon before 
arriving at the posterior abdominal wall. 

Usually a thin membrane, the greater omentum always 
contains an accumulation of fat, which may become sub¬ 
stantial in some individuals. Additionally, there are two 
arteries and accompanying veins, the right and left 
gastro-omental vessels, between this double-layered 
peritoneal apron just inferior to the greater curvature of 
the stomach. 

Lesser omentum 

The other two-layered peritoneal omentum is the lesser 
omentum (Fig. 4.5 7). It extends from the lesser curvature 
of the stomach and the first part of the duodenum to the 
inferior surface of the liver (Figs. 4.53 and 4.57). 

A thin membrane continuous with the peritoneal cover¬ 
ings of the anterior and posterior surfaces of the stomach 
and the first part of the duodenum, the lesser omentum is 
divided into: 


Liver Xiphoid process Stomach 



■ a medial hepatogastric ligament, which passes between 
the stomach and liver, and 

■ a lateral hepatoduodenal ligament, which passes 
between the duodenum and liver. 

The hepatoduodenal ligament ends laterally as a free 
margin and serves as the anterior border of the omental 
foramen (Fig. 4.54). Enclosed in this free edge are the 
hepatic artery proper, the bile duct, and the portal vein. 
Additionally, the right and left gastric vessels are between 
the layers of the lesser omentum near the lesser curvature 
of the stomach. 












Abdomen 


Gallbladder 


Omental foramen 
Duodenum 


Ascending colon 



■Stomach 


Descending colon 


Hepatogastric ligament 


Hepatoduodenal ligament 


Liver ( retracted) 


Lesser omentum 

Lesser curvature of the stomach 


Fig. 4.57 Lesser omentum. 


In the clinic 

The greater omentum 

When a laparotomy is performed and the peritoneal cavity 
is opened, the first structure usually encountered is the 
greater omentum. This fatty double-layered vascular 
membrane hangs like an apron from the greater curvature 
of the stomach, drapes over the transverse colon, and lies 
freely suspended within the abdominal cavity. It is often 
referred to as the "policeman of the abdomen" because of 
its apparent ability to migrate to any inflamed area and 
wrap itself around the organ to wall off inflammation. 
When a part of bowel becomes inflamed, it ceases 
peristalsis. This aperistaltic area is referred to as a local 
paralytic ileus. The remaining noninflamed part of the 


bowel continues to move and "massages" the greater 
omentum to the region where there is no peristalsis. The 
localized inflammatory reaction spreads to the greater 
omentum, which then adheres to the diseased area 
of bowel. 

The greater omentum is also an important site for 
metastatic tumor spread. Direct omental spread by a 
transcoelomic route is common for carcinoma of the 
ovary. As the metastases develop within the greater 
omentum, it becomes significantly thickened. 

In computed tomography imaging and during 
laparotomy, the thickened omentum is referred to 
as an "omental cake." 




























Regional anatomy • Abdominal Viscera 


Mesenteries 

Mesenteries are peritoneal folds that attach viscera to the 
posterior abdominal wall. They allow some movement and 
provide a conduit for vessels, nerves, and lymphatics to 
reach the viscera and include: 

■ the mesentery—associated with parts of the small 
intestine, 

■ the transverse mesocolon—associated with the trans¬ 
verse colon, and 

■ the sigmoid mesocolon—associated with the sigmoid 
colon. 

All of these are derivatives of the dorsal mesentery. 

Mesentery 

The mesentery is a large, fan-shaped, double-layered fold 
of peritoneum that connects the jejunum and ileum to the 
posterior abdominal wall (Fig. 4.58). Its superior attach¬ 
ment is at the duodenojejunal junction, just to the left of 
the upper lumbar part of the vertebral column. It passes 
obliquely downward and to the right, ending at the ileoce¬ 
cal junction near the upper border of the right sacro-iliac 
joint. In the fat between the two peritoneal layers of the 
mesentery are the arteries, veins, nerves, and lymphatics 
that supply the jejunum and ileum. 

Transverse mesocolon 

The transverse mesocolon is a fold of peritoneum that 
connects the transverse colon to the posterior abdominal 
wall (Fig. 4.58). Its two layers of peritoneum leave the pos¬ 
terior abdominal wall across the anterior surface of the 
head and body of the pancreas and pass outward to sur¬ 
round the transverse colon. Between its layers are the 
arteries, veins, nerves, and lymphatics related to the trans¬ 
verse colon. The anterior layer of the transverse mesocolon 
is adherent to the posterior layer of the greater omentum. 


Root of the transverse mesocolon 



Root of the mesentery- 


Root of the sigmoid mesocolon 


Fig. 4.58 Peritoneal reflections, forming mesenteries, outlined on 
the posterior abdominal wall. 


vertebra Sill. The sigmoid and superior rectal vessels, along 
with the nerves and lymphatics associated with the sigmoid 
colon, pass through this peritoneal fold. 


Sigmoid mesocolon 

The sigmoid mesocolon is an inverted, V-shaped perito¬ 
neal fold that attaches the sigmoid colon to the abdominal 
wall (Fig. 4.58). The apex of the V is near the division of 
the left common iliac artery into its internal and external 
branches, with the left limb of the descending V along the 
medial border of the left psoas major muscle and the right 
limb descending into the pelvis to end at the level of 


Ligaments 

Peritoneal ligaments consist of two layers of peritoneum 
that connect two organs to each other or attach an organ 
to the body wall, and may form part of an omentum. They 
are usually named after the structures being connected. 
For example, the splenorenal ligament connects the left 
kidney to the spleen and the gastrophrenic ligament con¬ 
nects the stomach to the diaphragm. 











310 


Abdomen 


Organs 

Abdominal esophagus 

The abdominal esophagus represents the short distal part 
of the esophagus located in the abdominal cavity. Emerg¬ 
ing through the right crus of the diaphragm, usually at the 
level of vertebra TX, it passes from the esophageal hiatus 
to the cardial orifice of the stomach just left of the midline 
(Fig. 4.59). 

Associated with the esophagus, as it enters the abdomi¬ 
nal cavity, are the anterior and posterior vagal trunks: 

■ The anterior vagal trunk consists of several smaller 
trunks whose fibers mostly come from the left vagus 
nerve; rotation of the gut during development moves 
these trunks to the anterior surface of the esophagus. 

■ Similarly, the posterior vagal trunk consists of a 
single trunk whose fibers mostly come from the right 
vagus nerve, and rotational changes during develop¬ 
ment move this trunk to the posterior surface of the 
esophagus. 



Fig. 4.59 Abdominal esophagus. 


The arterial supply to the abdominal esophagus 
(Fig. 4.60) includes: 

■ esophageal branches from the left gastric artery (from 
the celiac trunk), and 

■ esophageal branches from the left inferior phrenic 
artery (from the abdominal aorta). 

Stomach 

The stomach is the most dilated part of the gastrointestinal 
tract and has a J-like shape (Figs. 4.61 and 4.62). Posi¬ 
tioned between the abdominal esophagus and the small 
intestine, the stomach is in the epigastric, umbilical, and 
left hypochondrium regions of the abdomen. 

The stomach is divided into four regions: 

■ the cardia, which surrounds the opening of the esopha¬ 
gus into the stomach; 

■ the fundus of the stomach, which is the area above the 
level of the cardial orifice; 

■ the body of the stomach, which is the largest region of 
the stomach; and 

■ the pyloric part, which is divided into the pyloric antrum 
and pyloric canal and is the distal end of the stomach. 


Short gastric arteries 
Splenic artery 
Left gastric 



Posterior superior pancreaticoduodenal artery 
Anterior superior pancreaticoduodenal artery 
Gastroduodenal artery 


Fig. 4.60 Arterial supply to the abdominal esophagus and 
stomach. 






























Regional anatomy • Abdominal Viscera 



Abdominal 

esophagus 


Cardia 


Lesser curvature 


Angular incisure 
Pyloric orifice 


Cardial notch Fundus 


Greater 

curvature 


Pyloric sphincter 
Pyloric constriction 
Duodenum 


Body 
Pyloric antrum 


The most distal portion of the pyloric part of the stomach 
is the pylorus (Fig. 4.61). It is marked on the surface of the 
organ by the pyloric constriction and contains a thick¬ 
ened ring of gastric circular muscle, the pyloric sphinc¬ 
ter, that surrounds the distal opening of the stomach, the 
pyloric orifice (Figs. 4.61 and 4.62B). The pyloric orifice 
is just to the right of midline in a plane that passes through 
the lower border of vertebra LI (the transpyloric plane). 
Other features of the stomach include: 

■ the greater curvature, which is a point of attachment 
for the gastrosplenic ligament and the greater omentum; 

■ the lesser curvature, which is a point of attachment 
for the lesser omentum; 

■ the cardial notch, which is the superior angle created 
when the esophagus enters the stomach; and 

■ the angular incisure, which is a bend on the lesser 
curvature. 

The arterial supply to the stomach (Fig. 4.60) includes: 


Fig. 4.61 Stomach. 


■ the left gastric artery from the celiac trunk, 

■ the right gastric artery from the hepatic artery proper, 


Superior part of duodenum Esophagus 
Pyloric antrum 


Fundus of stomach 




Descending part of duodenum 


Body of stomach 
Duodenal jejunal flexure 


Pyloric sphincter Pyloric canal Inferior duodenum 


Fig. 4.62 Radiograph, using barium, showing the stomach and duodenum. A. Double-contrast radiograph of the stomach. B. Double-contrast 
radiograph showing the duodenal cap. 
































Abdomen 


■ the right gastro-omental artery from the gastroduode¬ 
nal artery, 

■ the left gastro-omental artery from the splenic artery, 
and 

■ the posterior gastric artery from the splenic artery 
(variant and not always present). 

Small intestine 

The small intestine is the longest part of the gastrointesti¬ 
nal tract and extends from the pyloric orifice of the 
stomach to the ileocecal fold. This hollow tube, which is 
approximately 6 to 7 m long with a narrowing diameter 
from beginning to end, consists of the duodenum, the 
jejunum, and the ileum. 

Duodenum 

The first part of the small intestine is the duodenum. This 
C-shaped structure, adjacent to the head of the pancreas, 
is 20 to 2 5 cm long and is above the level of the umbilicus; 
its lumen is the widest of the small intestine (Fig. 4.63). It 


is retroperitoneal except for its beginning, which is con¬ 
nected to the liver by the hepatoduodenal ligament, a part 
of the lesser omentum. 

The duodenum is divided into four parts (Fig. 4.63). 

■ The superior part (first part) extends from the pyloric 
orifice of the stomach to the neck of the gallbladder, is 
just to the right of the body of vertebra LI, and passes 
anteriorly to the bile duct, gastroduodenal artery, portal 
vein, and inferior vena cava. Clinically, the beginning of 
this part of the duodenum is referred to as the ampulla 
or duodenal cap, and most duodenal ulcers occur in this 
part of the duodenum. 

■ The descending part (second part) of the duodenum 
is just to the right of midline and extends from the neck 
of the gallbladder to the lower border of vertebra LIII. 
Its anterior surface is crossed by the transverse colon, 
posterior to it is the right kidney, and medial to it is 
the head of the pancreas. This part of the duodenum 
contains the major duodenal papilla, which is the 


Portal vein 
Right suprarenal gland 
Bile duct 

Duodenum 
—superior part 

Gallbladder 

Right kidney 

Position of minor 
duodenal papilla 

Position of major 
duodenal papilla 

Duodenum 
—descending part 

Duodenum 
—inferior part 

Ascending colon 



Inferior vena cava 


Esophagus 


Spleen 


Pancreas 

Left kidney 

Superior mesenteric 
vein and artery 

Descending colon 

Duodenum 
—ascending part 

Abdominal aorta 


312 


Fig. 4.63 Duodenum. 





































Regional anatomy • Abdominal Viscera 



common entrance for the bile and pancreatic ducts, and 
the minor duodenal papilla, which is the entrance for 
the accessory pancreatic duct, and the junction of the 
foregut and the midgut just below the major duodenal 
papilla. 

■ The inferior part (third part) of the duodenum is the 
longest section, crossing the inferior vena cava, the 
aorta, and the vertebral column (Figs. 4.62B and 4.63). 
It is crossed anteriorly by the superior mesenteric artery 
and vein. 

■ The ascending part (fourth part) of the duodenum 
passes upward on, or to the left of, the aorta to approxi¬ 
mately the upper border of vertebra LII and terminates 

at the duodenojejunal flexure. 

This duodenojejunal flexure is surrounded by a fold of 
peritoneum containing muscle fibers called the suspen¬ 
sory muscle (ligament) of duodenum (ligament of 
Treitz). 

The arterial supply to the duodenum (Fig. 4.64) 
includes: 


■ branches from the gastroduodenal artery, 

■ the supraduodenal artery from the gastroduodenal 
artery, 

■ duodenal branches from the anterior superior pancre¬ 
aticoduodenal artery (from the gastroduodenal artery), 

■ duodenal branches from the posterior superior pancre¬ 
aticoduodenal artery (from the gastroduodenal artery), 

■ duodenal branches from the anterior inferior pancreati¬ 
coduodenal artery (from the inferior pancreaticoduode¬ 
nal artery—a branch of the superior mesenteric artery), 

■ duodenal branches from the posterior inferior pancre¬ 
aticoduodenal artery (from the inferior pancreaticoduo¬ 
denal artery—a branch of the superior mesenteric 
artery), and 

■ the first jejunal branch from the superior mesenteric 
artery. 

Jejunum 

The jejunum and ileum make up the last two sections of 

the small intestine (Fig. 4.65). The jejunum represents the 

proximal two-fifths. It is mostly in the left upper quadrant 


Posterior superior 

pancreaticoduodenal artery Left gastric artery 


Hepatic artery proper 



Anterior superior 

pancreaticoduodenal 

artery 

Posterior inferior 
pancreaticoduodenal 
artery 


Supraduodenal 

artery 


Superior mesenteric 
artery 


Abdominal aorta 


Gastroduodenal 

artery 


Right gastro- 
omental artery 


Anterior inferior 
pancreaticoduodenal artery 


Fig. 4.64 Arterial supply to the duodenum. 


Jejunum 



Fig. 4.65 Radiograph, using barium, showing the jejunum and 
ileum. 


313 

























Abdomen 


of the abdomen and is larger in diameter and has a thicker 
wall than the ileum. Additionally, the inner mucosal lining 
of the jejunum is characterized by numerous prominent 
folds that circle the lumen (plicae circulares). The less 
prominent arterial arcades and longer vasa recta (straight 
arteries) compared to those of the ileum are a unique char¬ 
acteristic of the jejunum (Fig. 4.66). 

The arterial supply to the jejunum includes jejunal 
arteries from the superior mesenteric artery. 

Ileum 

The ileum makes up the distal three-filths of the small 
intestine and is mostly in the right lower quadrant. Com¬ 
pared to the jejunum, the ileum has thinner walls, fewer 
and less prominent mucosal folds (plicae circulares), 
shorter vasa recta, more mesenteric fat, and more arterial 
arcades (Fig. 4.66). 

The ileum opens into the large intestine, where the 
cecum and ascending colon join together. Two flaps pro¬ 
jecting into the lumen of the large intestine (the ileocecal 
fold) surround the opening (Fig. 4.67). The flaps of the 




Vasa recta 


Arterial arcades 




Ascending 

colon 


Ileum 


Ileocecal 
fold flaps 


Cecum 


Appendix 



Fig. 4.67 Ileocecal junction. A. Radiograph showing ileocecal 
junction. B. Illustration showing ileocecal junction and the 
ileocecal fold. C. Endoscopic image of the ileocecal fold. 


314 


Fig. 4.66 Differences in the arterial supply to the small intestine. 
A. Jejunum. B. Ileum. 
















Regional anatomy • Abdominal Viscera 


ileocecal fold come together at their end, forming ridges. 
Musculature from the ileum continues into each flap, 
forming a sphincter. Possible functions of the ileocecal fold 
include preventing reflux from the cecum to the ileum, and 
regulating the passage of contents from the ileum to the 
cecum. 

The arterial supply to the ileum (Fig. 4.68) includes: 

■ ileal arteries from the superior mesenteric artery, and 

■ an ileal branch from the ileocolic artery (from the supe¬ 
rior mesenteric artery). 

In the clinic 

Epithelial transition between the abdominal 
esophagus and stomach 

The gastroesophageal junction is demarcated by a 
transition from one epithelial type to another epithelial 
type. In some people, the histological junction does not 
lie at the physiological gastroesophageal junction but is 
in the lower one-third of the esophagus. This may 
predispose these people to esophageal ulceration and 
is also associated with an increased risk of 
adenocarcinoma. 


Superior mesenteric artery 



Jejunal and ileal arteries 
Fig. 4.68 Arterial supply to the ileum. 


In the clinic 
Duodenal ulceration 

Duodenal ulcers usually occur in the superior part of the 
duodenum and are much less common than they were 
50 years ago. At first, there was no treatment and patients 
died from hemorrhage or peritonitis. As surgical 
techniques developed, patients with duodenal ulcers were 
subjected to extensive upper gastrointestinal surgery 
to prevent ulcer recurrence and for some patients 
the treatment was dangerous. As knowledge and 
understanding of the mechanisms for acid secretion in the 
stomach increased, drugs were developed to block acid 
stimulation and secretion indirectly (histamine H 2 -receptor 
antagonists) and these have significantly reduced 
the morbidity and mortality rates of this disease. 
Pharmacological therapy can now directly inhibit the cells 
of the stomach that produce acid with, for example, 
proton pump inhibitors. Patients are also screened for the 
bacteria Helicobacter pylori, which when eradicated (by 
antibiotic treatment) significantly reduces duodenal ulcer 
formation. 

Anatomically, duodenal ulcers tend to occur either 
anteriorly or posteriorly. 


Posterior duodenal ulcers erode either directly onto the 
gastroduodenal artery or, more commonly, onto the 
posterior superior pancreaticoduodenal artery, which can 
produce torrential hemorrhage, which may be fatal in 
some patients. Treatment may involve extensive upper 
abdominal surgery with ligation of the vessels or by 
endovascular means whereby the radiologist may place a 
very fine catheter retrogradely from the femoral artery 
into the celiac artery. The common hepatic artery and the 
gastroduodenal artery are cannulated and the bleeding 
area may be blocked using small coils, which stem the 
flow of blood. 

Anterior duodenal ulcers erode into the peritoneal 
cavity, causing peritonitis. This intense inflammatory 
reaction and the local ileus promote adhesion of the 
greater omentum, which attempts to seal off the 
perforation. The stomach and duodenum usually contain 
considerable amounts of gas, which enters the peritoneal 
cavity and can be observed on a chest radiograph of an 
erect patient as subdiaphragmatic gas. In most instances, 
treatment for the ulcer is surgical. 








Abdomen 


In the clinic 

Examination of the upper gastrointestinal tract 

It is often necessary to examine the esophagus, stomach, 
duodenum, and proximal jejunum for disease. After taking 
an appropriate history and examining the patient, most 
physicians arrange a series of simple blood tests to look for 
bleeding, inflammation, and tumors. The next steps in the 
investigation assess the three components of any loop of 
bowel, namely, the lumen, the wall, and masses extrinsic 
to the bowel, which may compress or erode into it. 

Examination of the bowel lumen 

Barium sulfate solutions may be swallowed by the patient 
and can be visualized using an X-ray fluoroscopy unit. The 
lumen can be examined for masses (e.g., polyps and 
tumors) and peristaltic waves can be assessed. Patients 
may also be given carbon dioxide-releasing granules to 
fill the stomach so that the barium thinly coats the 
mucosa, resulting in images displaying fine mucosal detail. 
These tests are relatively simple and can be used to image 
the esophagus, stomach, duodenum, and small bowel. 

Examination of the bowel wall and extrinsic masses 
Endoscopy is a minimally invasive diagnostic medical 
procedure that can be used to assess the interior surfaces 
of an organ by inserting a tube into the body. The 
instrument is typically made of a flexible plastic material 
through which a light source and eyepiece are attached 
at one end. Some systems allow passage of small 
instruments through the main bore of the endoscope to 
obtain biopsies and to also undertake small procedures 
(e.g., the removal of polyps). 


In gastrointestinal and abdominal medicine an 
endoscope is used to assess the esophagus, stomach, 
duodenum, and proximal small bowel (Figs. 4.69 to 4.72). 
The tube is swallowed by the patient under light sedation 
and is extremely well tolerated. 

Assessment of the colon is performed by passage of 
the tube through the anus and into the rectum. The 
whole of the colon can be readily assessed; biopsies and 
the placement of stents can also be performed using this 
device. 



Fig.4.69 The endoscope is a flexible plastic tube that can be 
controlled from the proximal end. Through a side portal various 
devices can be inserted, which run through the endoscope 
and can be used to obtain biopsies and to perform minor 
endoluminal surgical procedures (e.g., excision of polyps). 


316 





Regional anatomy • Abdominal Viscera 


In the clinic—cont'd 



Fig. 4.70 Endoscopic images of the gastroesophageal junction. A. Normal. B. Esophageal cancer at esophageal junction. 



Fig. 4.71 Endoscopic image of the pyloric antrum of the Fig. 4.72 Endoscopic image showing normal appearance of the 

stomach looking toward the pylorus. second part of the duodenum. 



Abdomen 


In the clinic 
Meckel's diverticulum 

A Meckel's diverticulum (Fig. 4.73) is the remnant of the 
proximal part of the yolk stalk (vitelline duct) that extends 
into the umbilical cord in the embryo and lies on the 
antimesenteric border of the ileum. It appears as a 
blind-ended tubular outgrowth of bowel. Although it is an 


uncommon finding (occurring in approximately 2% of the 
population), it is always important to consider the 
diagnosis of Meckel's diverticulum because it does 
produce symptoms in a small number of patients. Typical 
findings include hemorrhage, intussusception, 
diverticulitis, ulceration, and obstruction. 




— Ileum 


Meckel's 

diverticulum 


Fig. 4.73 Vasculature associated with a Meckel’s diverticulum. A. Surgical image of Meckel’s diverticulum. B. Digital subtraction 
angiography. 


In the clinic In the clinic 


Computed tomography (CT) scanning and 
magnetic resonance imaging (MRI) 

These imaging techniques can provide important 
information about the wall of the bowel that may not 
be obtained from barium or endoscopic studies. 
Thickening of the wall may indicate inflammatory 
change or tumor and is always regarded with suspicion. 
If a tumor is demonstrated, the locoregional spread can 
be assessed, along with lymphadenopathy and 
metastatic spread. 

Advanced imaging methods 

A small ultrasound device placed on the end of the 
endoscope can produce extremely high-powered 
views of the mucosa and submucosa of the upper 
gastrointestinal tract. These views can show whether a 
tumor is resectable and guide the clinician in taking a 
biopsy. 


Carcinoma of the stomach 

Carcinoma of the stomach is a common gastrointestinal 
malignancy. Chronic gastric inflammation (gastritis), 
pernicious anemia, and polyps predispose to the 
development of this aggressive cancer, which is usually 
not diagnosed until late in the course of the disease. 
Symptoms include vague epigastric pain, early fullness 
with eating, bleeding leading to chronic anemia, and 
obstruction. 

The diagnosis may be made using barium and 
conventional radiology or endoscopy, which allows a 
biopsy to be obtained at the same time. Ultrasound 
scanning is used to check the liver for metastatic 
spread, and, if negative, computed tomography is 
carried out to assess for surgical resectability. If 
carcinoma of the stomach is diagnosed early, a curative 
surgical resection is possible. However, because most 
patients do not seek treatment until late in the disease, 
the overall 5-year survival rate is between 5% and 20%, 
with a mean survival time of between 5 and 8 months. 








Regional anatomy • Abdominal Viscera 


Large intestine 

The large intestine extends from the distal end of the ileum 
to the anus, a distance of approximately 1.5 m in adults. It 
absorbs fluids and salts from the gut contents, thus forming 
feces, and consists of the cecum, appendix, colon, rectum, 
and anal canal (Figs. 4.74 and 4.75). 

Beginning in the right groin as the cecum, with its asso¬ 
ciated appendix, the large intestine continues upward as 


the ascending colon through the right flank and into the 
right hypochondrium (Fig. 4.76). Just below the liver, it 
bends to the left, forming the right colic flexure (hepatic 
flexure), and crosses the abdomen as the transverse 
colon to the left hypochondrium. At this position, just 
below the spleen, the large intestine bends downward, 
forming the left colic flexure (splenic flexure), and con¬ 
tinues as the descending colon through the left flank and 
into the left groin. 



Right colic flexure 


Ascending colon 


Taeniae coli 


Transverse colon 


Left colic flexure 


Omental appendices 


Haustra of colon 


Cecum 


Appendix 


Rectum 


Anal canal 


Fig. 4.74 Large intestine. 



















Abdomen 


Ascending colon Transverse colon Descending colon 



Sigmoid colon Rectum 

Fig. 4.75 Radiograph, using barium, showing the large intestine. 


Right Midclavicular planes Left 

hypochondrium i _ I hypochondrium 



Intertubercular plane Subcostal plane 


Fig. 4.76 Position of the large intestine in the nine-region 
organizational pattern. 


It enters the upper part of the pelvic cavity as the 

sigmoid colon, continues on the posterior wall of the pelvic Ascending colon Ileum Appendix 

cavity as the rectum, and terminates as the anal canal. 

The general characteristics of most of the large intestine 
(Fig. 4.74) are: 

■ its large internal diameter compared to that of the small 
intestine; 

■ peritoneal-covered accumulations of fat (the omental 
appendices) are associated with the colon; 

■ the segregation of longitudinal muscle in its walls into 
three narrow bands (the taeniae coli), which are pri¬ 
marily observed in the cecum and colon and less visible 
in the rectum; and 

■ the sacculations of the colon (the haustra of the 
colon). 

Cecum and appendix 

The cecum is the first part of the large intestine (Fig. 

4.77). It is inferior to the ileocecal opening and in the right 
iliac fossa. It is an intraperitoneal structure because of its 
mobility, not because of its suspension by a mesentery. 

The cecum is continuous with the ascending colon at 
320 the entrance of the ileum and is usually in contact with Flg * 4,77 Cecum and a PP endlx * 



Taeniae 

coli 


Cecum 






































Regional anatomy • Abdominal Viscera 



the anterior abdominal wall. It may cross the pelvic brim 
to lie in the true pelvis. The appendix is attached to the 
posteromedial wall of the cecum, just inferior to the end of 
the ileum (Fig. 4.77). 

The appendix is a narrow, hollow, blind-ended tube 
connected to the cecum. It has large aggregations of lym¬ 
phoid tissue in its walls and is suspended from the terminal 
ileum by the mesoappendix (Fig. 4.78), which contains 
the appendicular vessels. Its point of attachment to the 
cecum is consistent with the highly visible free taeniae 
leading directly to the base of the appendix, but the 
location of the rest of the appendix varies considerably 
(Fig. 4.79). It may be: 

■ posterior to the cecum or the lower ascending colon, or 
both, in a retrocecal or retrocolic position; 

■ suspended over the pelvic brim in a pelvic or descending 
position; 

■ below the cecum in a subcecal location; or 

■ anterior to the terminal ileum, possibly contacting the 
body wall, in a pre-ileal position or posterior to the ter¬ 
minal ileum in a postileal position. 

The surface projection of the base of the appendix is at 
the junction of the lateral and middle one-third of a line 
from the anterior superior iliac spine to the umbilicus 
(McBurney’s point). People with appendicular problems 
may describe pain near this location. 

The arterial supply to the cecum and appendix (Fig. 
4.80) includes: 


Taeniae coli 



■ the anterior cecal artery from the ileocolic artery 
(from the superior mesenteric artery), 

■ the posterior cecal artery from the ileocolic artery 
(from the superior mesenteric artery), and 

■ the appendicular artery from the ileocolic artery 
(from the superior mesenteric artery). 


Taeniae coli 



Subcecal 


Fig. 4.79 Positions of the appendix. 



Fig. 4.80 Arterial supply to the cecum and appendix. 


321 


















Abdomen 


In the clinic 

Appendicitis 

Acute appendicitis is an abdominal emergency. It 
usually occurs when the appendix is obstructed by 
either a fecalith or enlargement of the lymphoid 
nodules. Within the obstructed appendix, bacteria 
proliferate and invade the appendix wall, which 
becomes damaged by pressure necrosis. In some 
instances, this may resolve spontaneously; in other 
cases, inflammatory change (Fig. 4.81) continues and 
perforation ensues, which may lead to localized or 
generalized peritonitis. 

Most patients with acute appendicitis have localized 
tenderness in the right groin. Initially, the pain begins as 
a central, periumbilical, colicky type of pain, which 
tends to come and go. After 6 to 10 hours, the pain 
tends to localize in the right iliac fossa and becomes 
constant. Patients may develop a fever, nausea, and 
vomiting. The etiology of the pain for appendicitis is 
described in Case 1 of Chapter 1 on p. 50. 

The treatment for appendicitis is appendectomy. 


Thickened wall 



Fig. 4.81 Inflamed appendix. Ultrasound scan. 


Right paracolic gutter Descending colon 


Transverse colon 


Left paracolic gutter 




Colon 

The colon extends superiorly from the cecum and consists 
of the ascending, transverse, descending, and sigmoid 
colon (Fig. 4.82). Its ascending and descending segments 
are (secondarily) retroperitoneal and its transverse and 
322 sigmoid segments are intraperitoneal. 


Fig. 4.82 Colon. 

At the junction of the ascending and transverse colon 
is the right colic flexure, which is just inferior to the right 
lobe of the liver (Fig. 4.83). A similar, but more acute bend 
(the left colic flexure) occurs at the junction of the trans¬ 
verse and descending colon. This bend is just inferior to the 




























Regional anatomy • Abdominal Viscera 



spleen, is higher and more posterior than the right colic 
flexure, and is attached to the diaphragm by the phrenico- 
colic ligament. 

Immediately lateral to the ascending and descending 
colon are the right and left paracolic gutters (Fig. 4.8 2 ). 
These depressions are formed between the lateral margins 
of the ascending and descending colon and the posterolat¬ 
eral abdominal wall and are gutters through which mate¬ 
rial can pass from one region of the peritoneal cavity to 
another. Because major vessels and lymphatics are on 
the medial or posteromedial sides of the ascending and 
descending colon, a relatively blood-free mobilization of the 
ascending and descending colon is possible by cutting the 
peritoneum along these lateral paracolic gutters. 

The final segment of the colon (the sigmoid colon) 
begins above the pelvic inlet and extends to the level of 
vertebra Sill, where it is continuous with the rectum 
(Fig. 4.82). This S-shaped structure is quite mobile except 
at its beginning, where it continues from the descending 
colon, and at its end, where it continues as the rectum. 
Between these points, it is suspended by the sigmoid 
mesocolon. 

The arterial supply to the ascending colon (Fig. 4.84) 
includes: 

■ the colic branch from the ileocolic artery (from the supe¬ 
rior mesenteric artery), 

■ the anterior cecal artery from the ileocolic artery (from 
the superior mesenteric artery), 


Liver 


Spleen 



Left colic flexure 


■ the posterior cecal artery from the ileocolic artery (from 
the superior mesenteric artery), and 

■ the right colic artery from the superior mesenteric 
artery. 

The arterial supply to the transverse colon (Fig. 4.84) 
includes: 

■ the right colic artery from the superior mesenteric 
artery, 

■ the middle colic artery from the superior mesenteric 
artery, and 

■ the left colic artery from the inferior mesenteric artery. 

The arterial supply to the descending colon (Fig. 4.84) 
includes the left colic artery from the inferior mesenteric 
artery. 

The arterial supply to the sigmoid colon (Fig. 4.84) 
includes sigmoidal arteries from the inferior mesenteric 
artery. 


Superior mesenteric artery 
Middle colic artery 
Arteria recta 


Inferior mesenteric artery 
Left colic artery 
Marginal artery 



Ileocolic artery 
Right colic artery 


Arteria recta 
Sigmoid arteries 


Superior rectal artery 


Fig. 4.84 Arterial supply to the colon. 


Right colic flexure Transverse colon 
Fig. 4.83 Right and left colic flexures. 


323 





























Abdomen 


Rectum and anal canal 

Extending from the sigmoid colon is the rectum (Fig. 4.85). 
The rectosigmoid junction is usually described as being at 
the level of vertebra Sill or at the end of the sigmoid meso¬ 
colon because the rectum is a retroperitoneal structure. 

The anal canal is the continuation of the large intestine 
inferior to the rectum. 

The arterial supply to the rectum and anal canal (Fig. 
4.86) includes: 

■ the superior rectal artery from the inferior mesenteric 
artery 

■ the middle rectal artery from the internal iliac artery 
and 

■ the inferior rectal artery from the internal pudendal 
artery (from the internal iliac artery). 



Right common iliac artery 

Left common iliac artery 

Left internal iliac artery 



-Inferior rectal artery- 

-Internal pudendal artery- 

-Middle rectal artery- 

Fig. 4.86 Arterial supply to the rectum and anal canal. Posterior 
view. 


Fig. 4.85 Rectum and anal canal. 


324 



































Regional anatomy • Abdominal Viscera 


In the clinic 

Congenital disorders of the gastrointestinal tract 

The normal positions of the abdominal viscera result from 
a complex series of rotations that the gut tube undergoes 
and from the growth of the abdominal cavity to 
accommodate changes in the size of the developing 
organs (see pp. 265-268). A number of developmental 
anomalies can occur during gut development, many of 
which appear in the neonate or infant, and some of which 
are surgical emergencies. Occasionally, such disorders are 
diagnosed only in adults. 

Malrotation and midgut volvulus 

Mai rotation is incomplete rotation and fixation of the 
midgut after it has passed from the umbilical sac and 
returned to the abdominal coelom (Figs. 4.87 and 4.88). 


Stomach Pylorus Duodenum 



Ribbon-twisted duodenum and proximal jejunum 

Fig. 4.87 Small bowel malrotation and volvulus. Radiograph of 
stomach, duodenum, and upper jejunum using barium. 


The proximal attachment of the small bowel mesentery 
begins at the suspensory muscle of duodenum 
(ligament of Treitz), which determines the position of the 
duodenojejunal junction. The mesentery of the small 
bowel ends at the level of the ileocecal junction in the 
right lower quadrant. This long line of fixation of the 
mesentery prevents accidental twists of the gut. 

If the duodenojejunal flexure or the cecum does not 
end up in its usual site, the origin of the small bowel 
mesentery shortens, which permits twisting of the small 
bowel around the axis of the superior mesenteric artery. 
Twisting of the bowel, in general, is termed volvulus. 
Volvulus of the small bowel may lead to a reduction of 
blood flow and infarction. 

In some patients, the cecum ends up in the 
midabdomen. From the cecum and the right side of the 
colon a series of peritoneal folds (Ladd's bands) develop 
that extend to the right undersurface of the liver and 
compress the duodenum. A small bowel volvulus may 
then occur as well as duodenal obstruction. Emergency 
surgery may be necessary to divide the bands. 



Jejunum 


Fig. 4.88 Small bowel malrotation. Radiograph of stomach, 
duodenum, and jejunum using barium. 






Abdomen 


In the clinic 
Bowel obstruction 

A bowel obstruction can be either functional or due to a 
true obstruction. Mechanical obstruction is caused by an 
intraluminal, mural, or extrinsic mass which can be 
secondary to a foreign body, obstructing tumor in the 
wall, or extrinsic compression from an adhesion, or 
embryological band (Fig. 4.89). 

A functional obstruction is usually due to an inability of 
the bowel to peristalse, which again has a number of 
causes, and most frequently is a postsurgical state due to 
excessive intraoperative bowel handling. Other causes 
may well include abnormality of electrolytes (e.g., sodium 
and potassium) rendering the bowel paralyzed until 
correction has occurred. 

The signs and symptoms of obstruction depend on the 
level at which the obstruction has occurred. The primary 
symptom is central abdominal, intermittent, colicky pain 
as the peristaltic waves try to overcome the obstruction. 
Abdominal distention will occur if it is a low obstruction 
(distal), allowing more proximal loops of bowel to fill with 

r Plicae circulares 


*/■ 


\ 

\ 


L Dilation of small bowel 

Fig. 4.89 This radiograph of the abdomen, anteroposterior 
view, demonstrates a number of dilated loops of small bowel. 
Small bowel can be identified by the plicae circulares that pass 
from wall to wall as indicated. The large bowel is not dilated. 
The cause of the small bowel dilatation is an adhesion after 
pelvic surgery. 


fluid. A high obstruction (in the proximal small bowel) 
may not produce abdominal distention. 

Vomiting and absolute constipation, including the 
inability to pass flatus, will ensue. 

Early diagnosis is important because considerable fluid 
and electrolytes enter the bowel lumen and fail to be 
reabsorbed, which produces dehydration and electrolyte 
abnormalities. Furthermore, the bowel continues to 
distend, compromising the blood supply within the bowel 
wall, which may lead to ischemia and perforation. The 
symptoms and signs are variable and depend on the level 
of obstruction. 

Small bowel obstruction is typically caused by 
adhesions following previous surgery, and history should 
always be sought for any operations or abdominal 
interventions (e.g., previous appendectomy). Other causes 
include bowel passing into hernias (e.g., inguinal) and 
bowel twisting on its own mesentery (volvulus). 
Examination of hernial orifices is mandatory in patients 
with bowel obstruction. 

Large bowel obstruction is commonly caused by a 
tumor. Other potential causes include hernias and 
inflammatory diverticular disease of the sigmoid colon. 

The treatment is intravenous replacement of fluid and 
electrolytes, analgesia, and relief of obstruction. The 
passage of a nasogastric tube allows aspiration of fluid 
from the stomach. In many instances, small bowel 
obstruction, typically secondary to adhesions, will settle 
with nonoperative management. Large bowel obstruction 
may require an urgent operation to remove the 
obstructing lesion, or a temporary bypass procedure (e.g., 
defunctioning colostomy) (Fig. 4.90). 


L Distal large bowel L Colonic stent L Rectum 

Fig. 4.90 This oblique radiograph demonstrates contrast 
passing through a colonic stent that has been placed to relieve 
bowel obstruction prior to surgery. 


326 




Regional anatomy • Abdominal Viscera 


In the clinic 


Diverticular disease 

Diverticular disease is the development of multiple colonic 
diverticula, predominantly throughout the sigmoid colon, 
though the whole colon may be affected (Fig. 4.91 ). The 
sigmoid colon has the smallest diameter of any portion of 
the colon and is therefore the site where intraluminal 
pressure is potentially the highest. Poor dietary fiber 
intake and obesity are also linked to diverticular disease. 

The presence of multiple diverticula does not 
necessarily mean the patient requires any treatment. 
Moreover, many patients have no other symptoms or 
signs. 

Patients tend to develop symptoms and signs when 
the neck of the diverticulum becomes obstructed by feces 
and becomes infected. Inflammation may spread along 
the wall, causing abdominal pain. When the sigmoid colon 
becomes inflamed (diverticulitis), abdominal pain and 
fever ensue. 

Because of the anatomical position of the sigmoid 
colon there are a number of complications that may 
occur. The diverticula can perforate to form an abscess in 
the pelvis. The inflammation may produce an 
inflammatory mass, obstructing the left ureter. 
Inflammation may also spread to the bladder, producing a 
fistula between the sigmoid colon and the bladder. In 
these circumstances patients may develop a urinary tract 
infection and rarely have fecal material and gas passing 
per urethra. 

The diagnosis is based upon clinical examination and 
often CT scanning. In the first instance, patients will be 
treated with antibiotic therapy; however, a surgical 
resection may be necessary if symptoms persist. 


Descending colon 



Fig. 4.91 This double-contrast barium enema demonstrates 
numerous small outpouchings throughout the distal large 
bowel predominantly within the descending colon and the 
sigmoid colon. These small outpouchings are diverticula and in 
most instances remain quiescent. 


In the clinic 
Ostomies 

It is occasionally necessary to surgically externalize bowel 
to the anterior abdominal wall. Externalization of bowel 
plays an important role in patient management. These 
extraanatomical bypass procedures use our anatomical 
knowledge and in many instances are life saving. 

Gastrostomy 

Gastrostomy is performed when the stomach is attached 
to the anterior abdominal wall and a tube is placed 
through the skin into the stomach. Typically this is 
performed to feed the patient when it is impossible to 
take food and fluid orally (e.g., complex head and neck 
cancer). The procedure can be performed either surgically 
or through a direct needlestick puncture under sedation 
in the anterior abdominal wall. 


Jejunostomy 

Similarly the jejunum is brought to the anterior abdominal 
wall and fixed. The jejunostomy is used as a site where a 
feeding tube is placed through the anterior abdominal 
wall into the proximal efferent small bowel. 

Ileostomy 

An ileostomy is performed when small bowel contents 
need to be diverted from the distal bowel. An ileostomy is 
often performed to protect a distal surgical anastomosis, 
such as in the colon to allow healing after surgery. 

Colostomy 

There are a number of instances when a colostomy may 
be necessary. In many circumstances it is performed to 
protect the distal large bowel after surgery. A further 

(continues) 



Abdomen 


In the clinic—cont'd 

indication would include large bowel obstruction with 
imminent perforation wherein a colostomy allows 
decompression of the bowel and its contents. This is a 
safe and temporizing procedure performed when the 
patient is too unwell for extensive bowel surgery. It is 
relatively straightforward and carries reduced risk, 
preventing significant morbidity and mortality. 

An end colostomy is necessary when the patient has 
undergone a surgical resection of the rectum and anus 
(typically for cancer). 

Ileal conduit 

An ileal conduit is an extraanatomical procedure and is 
performed after resection of the bladder for tumor. In this 
situation a short segment of small bowel is identified. The 


bowel is divided twice to produce a 20-cm segment of 
small bowel on its own mesentery. This isolated segment 
of bowel is used as a conduit. The remaining bowel is 
joined together. The proximal end is anastomosed to the 
ureters, and the distal end is anastomosed to the anterior 
abdominal wall. Hence, urine passes from the kidneys into 
the ureters and through the short segment of small bowel 
to the anterior abdominal wall. 

When patients have either an ileostomy, colostomy, or 
ileal conduit it is necessary for them to fix a collecting bag 
onto the anterior abdominal wall. Contrary to one's initial 
thoughts these bags are tolerated extremely well by most 
patients and allow patients to live a nearly normal and 
healthy life. 


Liver 

The liver is the largest visceral organ in the body and is 
primarily in the right hypochondrium and epigastric 
region, extending into the left hypochondrium (or in the 
right upper quadrant, extending into the left upper quad¬ 
rant) (Fig. 4.92). 

Surfaces of the liver include: 

■ a diaphragmatic surface in the anterior, superior, and 
posterior directions; and 

■ a visceral surface in the inferior direction (Fig. 4.93). 


Diaphragmatic surface 

The diaphragmatic surface of the liver, which is smooth 
and domed, lies against the inferior surface of the dia¬ 
phragm (Fig. 4.94). Associated with it are the subphrenic 
and hepatorenal recesses (Fig. 4.93): 

■ The subphrenic recess separates the diaphragmatic 
surface of the liver from the diaphragm and is divided 
into right and left areas by the falciform ligament, a 
structure derived from the ventral mesentery in the 
embryo. 

■ The hepatorenal recess is a part of the peritoneal cavity 
on the right side between the liver and the right kidney 
and right suprarenal gland. 



Liver 


Midclavicular planes 

I 


Subcostal plane 


Intertubercular plane 


The subphrenic and hepatorenal recesses are continu- Fig. 4.92 Position of the liver in the abdomen, 
ous anteriorly. 


328 

















Regional anatomy • Abdominal Viscera 



Liver 


Subphrenic recess 



Falciform 

ligament 


Gallbladder 


Right lobe 


Left lobe Diaphragm 


Fig. 4.94 Diaphragmatic surface of the liver. 














Abdomen 


Visceral surface 

The visceral surface of the liver is covered with visceral 
peritoneum except in the fossa for the gallbladder and 
at the porta hepatis (gateway to the liver; Fig. 4.95), and 
structures related to it include the following (Fig. 4.96): 

■ esophagus, 

■ right anterior part of the stomach, 

■ superior part of the duodenum, 

■ lesser omentum, 

■ gallbladder, 


■ right colic flexure, 

■ right transverse colon, 

■ right kidney, and 

■ right suprarenal gland. 

The porta hepatis serves as the point of entry into the 
liver for the hepatic arteries and the portal vein, and the 
exit point for the hepatic ducts (Fig. 4.95). 

Associated ligaments 

The liver is attached to the anterior abdominal wall by the 
falciform ligament and, except for a small area of the 


A 



Fissure for ligamentum teres 


Porta hepatis 
Cystic duct 


Gallbladder 


i— Fundus 
Body 
- Neck 


Right lobe 
of liver 


Left lobe of liver 


Bile duct- 

Portal vein 


Hepatic artery proper 


Caudate lobe 


Fissure for ligamentum 
venosum 


Hepatic ducts 


Quadrate lobe 


Quadrate lobe 
Gallbladder 
Portal vein 

Inferior vena cava 

Right lobe of liver 
Right crus 



Fig. 4.95 Visceral surface of the liver. A. Illustration. B. Abdominal computed tomogram, with contrast, in the axial plane. 




































Regional anatomy • Abdominal Viscera 



liver against the diaphragm (the bare area), the liver is 
almost completely surrounded by visceral peritoneum (Fig. 
4.96). Additional folds of peritoneum connect the liver to 
the stomach (hepatogastric ligament), the duodenum 
(hepatoduodenal ligament), and the diaphragm (right 
and left triangular ligaments and anterior and poste¬ 
rior coronary ligaments). 

The bare area of the liver is a part of the liver on the 
diaphragmatic surface where there is no intervening peri¬ 
toneum between the liver and the diaphragm (Fig. 4.96): 

■ The anterior boundary of the bare area is indicated by 
a reflection of peritoneum—the anterior coronary 
ligament. 

■ The posterior boundary of the bare area is indicated by 
a reflection of peritoneum—the posterior coronary 
ligament. 

■ Where the coronary ligaments come together laterally, 
they form the right and left triangular ligaments. 

Lobes 

The liver is divided into right and left lobes by fossae for the 
gallbladder and the inferior vena cava (Fig. 4.95). The 
right lobe of the liver is the largest lobe, whereas the left 
lobe of the liver is smaller. The quadrate and caudate 
lobes are described as arising from the right lobe of the liver 
but functionally are distinct. 


■ The quadrate lobe is visible on the anterior part of the 
visceral surface of the liver and is bounded on the left by 
the fissure for the ligamentum teres and on the right 
by the fossa for the gallbladder. Functionally, it is related 
to the left lobe of the liver. 

■ The caudate lobe is visible on the posterior part of the 
visceral surface of the liver. It is bounded on the left by 
the fissure for the ligamentum venosum and on the right 
by the groove for the inferior vena cava. Functionally, it 
is separate from the right and the left lobes of the liver. 

The arterial supply to the liver includes: 

■ the right hepatic artery from the hepatic artery proper 
(a branch of the common hepatic artery from the celiac 
trunk), and 

■ the left hepatic artery from the hepatic artery proper (a 
branch of the common hepatic artery from the celiac 
trunk). 

Gallbladder 

The gallbladder is a pear-shaped sac lying on the visceral 

surface of the right lobe of the liver in a fossa between the 

right and quadrate lobes (Fig. 4.95). It has: 

■ a rounded end (fundus of the gallbladder), which 
may project from the inferior border of the liver; 



Colic impression 


Posterior coronary ligament 


Left triangular ligament 


Falciform ligament 


Caudate lobe 

Inferior vena cava 

Suprarenal impression 

Bare area 

Anterior coronary ligament 


Gastric impression 

Left lobe of liver 
Esophageal impression 


Right triangular 
ligament 

Renal impression 

Right lobe of liver 
Neck 

Body L- Gallbladder 


Porta hepatis 


Quadrate 


lobe 


Fundus 


Fig. 4.96 Posterior view of the bare area of the liver and associated ligaments. 


331 
















Abdomen 


■ a major part in the fossa (body of the gallbladder), 
which may be against the transverse colon and the 
superior part of the duodenum; and 

■ a narrow part (neck of the gallbladder) with mucosal 
folds forming the spiral fold. 


The arterial supply to the gallbladder (Fig. 4.97) is the 
cystic artery from the right hepatic artery (a branch of the 
hepatic artery proper). 

The gallbladder receives, concentrates, and stores bile 
from the liver. 


Left hepatic artery Left gastric artery 


A 


Right hepatic artery 


Hepatic artery proper 



Cystic 


Supraduodenal artery 

Gastroduodenal artery 
Right gastric artery- 

Abdominal aorta 
Superior mesenteric artery 

Splenic artery 


Liver Gallbladder 



Cystic duct Cystic artery 


Fig. 4.97 Arterial supply to the liver and gallbladder. A. Schematic. B. Laparoscopic surgical view of cystic duct and cystic artery. 


332 
















Regional anatomy • Abdominal Viscera 


Pancreas 

The pancreas lies mostly posterior to the stomach 
(Figs. 4.98 and 4.99). It extends across the posterior 
abdominal wall from the duodenum, on the right, to the 
spleen, on the left. 


The pancreas is (secondarily) retroperitoneal except for 
a small part of its tail and consists of a head, uncinate 
process, neck, body, and tail. 

■ The head of the pancreas lies within the C-shaped 
concavity of the duodenum. 



Fig. 4.98 Pancreas. 











Abdomen 


Pancreas 


Stomach 



Right lobe of liver 

Inferior vena cava 
Right crus 


Left kidney 

Aorta Spleen 

Left crus 



Fig. 4.99 Abdominal images. A. Abdominal computed tomogram, with contrast, in the axial plane. B. Abdominal ultrasound scan. 


334 


















Regional anatomy • Abdominal Viscera 


■ Projecting from the lower part of the head is the unci¬ 
nate process, which passes posterior to the superior 
mesenteric vessels. 

■ The neck of the pancreas is anterior to the superior 
mesenteric vessels. Posterior to the neck of the pan¬ 
creas, the superior mesenteric and splenic veins join to 
form the portal vein. 

■ The body of the pancreas is elongate and extends 
from the neck to the tail of the pancreas. 

■ The tail of the pancreas passes between layers of the 
splenorenal ligament. 

The pancreatic duct begins in the tail of the pancreas 
(Fig. 4.100). It passes to the right through the body of the 
pancreas and, after entering the head of the pancreas, 
turns inferiorly. In the lower part of the head of the pan¬ 
creas, the pancreatic duct joins the bile duct. The joining 
of these two structures forms the hepatopancreatic 
ampulla (ampulla of Vater), which enters the descending 
(second) part of the duodenum at the major duodenal 


papilla. Surrounding the ampulla is the sphincter of 
ampulla (sphincter of Oddi), which is a collection of 
smooth muscles. 

The accessory pancreatic duct empties into the duo¬ 
denum just above the major duodenal papilla at the minor 
duodenal papilla (Fig. 4.100). If the accessory duct is 
followed from the minor papilla into the head of the pan¬ 
creas, a branch point is discovered: 

■ One branch continues to the left, through the head of 
the pancreas, and may connect with the pancreatic duct 
at the point where it turns inferiorly. 

■ A second branch descends into the lower part of the 
head of the pancreas, anterior to the pancreatic duct, 
and ends in the uncinate process. 

The main and accessory pancreatic ducts usually com¬ 
municate with each other. The presence of these two ducts 
reflects the embryological origin of the pancreas from 
dorsal and ventral buds from the foregut. 



Major duodenal papilla 


Accessory pancreatic duct 


Minor duodenal papilla 


Main pancreatic duct 


Hepatopancreatic ampulla 


Fig. 4.100 Pancreatic duct system. 










Abdomen 


The arterial supply to the pancreas (Fig. 4.101) 

includes the: 

■ gastroduodenal artery from the common hepatic artery 
(a branch of the celiac trunk), 

■ anterior superior pancreaticoduodenal artery from the 
gastroduodenal artery, 

■ posterior superior pancreaticoduodenal artery from the 
gastroduodenal artery, 

■ dorsal pancreatic artery from the inferior pancreatic 
artery (a branch of the splenic artery), 

■ great pancreatic artery from the inferior pancreatic 
artery (a branch of the splenic artery), 

■ anterior inferior pancreaticoduodenal artery from the 
inferior pancreaticoduodenal artery (a branch of the 
superior mesenteric artery), and 

■ posterior inferior pancreaticoduodenal artery from 
the inferior pancreaticoduodenal artery (a branch of 
the superior mesenteric artery). 


In the clinic 

Annular pancreas 

The pancreas develops from ventral and dorsal buds 
from the foregut. The dorsal bud forms most of the 
head, neck, and body of the pancreas. The ventral bud 
rotates around the bile duct to form part of the head 
and the uncinate process. If the ventral bud splits 
(becomes bifid), the two segments may encircle the 
duodenum. The duodenum is therefore constricted and 
may even undergo atresia, and be absent at birth 
because of developmental problems. After birth, the 
child may fail to thrive and may vomit due to poor 
gastric emptying. 

Sometimes an annular pancreas is diagnosed in 
utero by ultrasound scanning. The obstruction of the 
duodenum may prevent the fetus from swallowing 
enough amniotic fluid, which may increase the overall 
volume of amniotic fluid in the amniotic sac 
surrounding the fetus (polyhydramnios). 


Left gastro-omental artery 


Splenic artery Left gastric artery 



Greater pancreatic 
artery 


Celiac trunk 

Common hepatic 
artery 

Gastroduodenal 


Dorsal pancreatic 
artery 


Inferior 

pancreaticoduodenal artery 


Anterior inferior 
pancreaticoduodenal artery 


Posterior inferior 
pancreaticoduodenal artery 


Superior mesenteric artery 


Posterior superior pancreaticoduodenal artery 


Fig. 4.101 Arterial supply to the pancreas. Posterior view. 


In the clinic 

Pancreatic cancer 

Pancreatic cancer accounts for a significant number of 
deaths and is often referred to as the "silent killer." 
Malignant tumors of the pancreas may occur anywhere 
within the pancreas but are most frequent within the 
head and the neck. There are a number of nonspecific 
findings in patients with pancreatic cancer, including 
upper abdominal pain, loss of appetite, and weight loss. 
Depending on the exact site of the cancer, obstruction 
of the bile duct may occur, which can produce 
obstructive jaundice. Although surgery is indicated in 
patients where there is a possibility of cure, most 
detected cancers have typically spread locally, invading 
the portal vein and superior mesenteric vessels, and 
may extend into the porta hepatis. Lymph node spread 
also is common and these factors would preclude 
curative surgery. 

Given the position of the pancreas, a surgical 
resection is a complex procedure involving resection of 
the region of pancreatic tumor usually with part of the 
duodenum, necessitating a complex bypass procedure. 


336 














Regional anatomy • Abdominal Viscera 


Duct system for bile 

The duct system for the passage of bile extends from the 
liver, connects with the gallbladder, and empties into the 
descending part of the duodenum (Fig. 4.102). The coales¬ 
cence of ducts begins in the liver parenchyma and contin¬ 
ues until the right and left hepatic ducts are formed. 
These drain the respective lobes of the liver. 

The two hepatic ducts combine to form the common 
hepatic duct, which runs near the liver, with the hepatic 
artery proper and portal vein in the free margin of the 
lesser omentum. 


As the common hepatic duct continues to descend, it 
is joined by the cystic duct from the gallbladder. This 
completes the formation of the bile duct. At this point, 
the bile duct lies to the right of the hepatic artery 
proper and usually to the right of, and anterior to, the 
portal vein in the free margin of the lesser omentum. 
The omental foramen is posterior to these structures at 
this point. 

The bile duct continues to descend, passing posteriorly 
to the superior part of the duodenum before joining with 
the pancreatic duct to enter the descending part of the 
duodenum at the major duodenal papilla (Fig. 4.102). 



Gallbladder 


Right hepatic duct 


Cystic duct 


Bile duct 


Needle 


Left hepatic duct 
Common hepatic duct 


Cystic duct 


Descending 
part of 
duodenum 


Descending part of duodenum 


Main pancreatic duct 


Common 
hepatic duct 


Bile duct 


Fig. 4.102 Bile drainage. A. Duct system for passage of bile. B. Percutaneous transhepatic cholangiogram demonstrating the bile duct 
system. 









Abdomen 


Spleen 

The spleen develops as part of the vascular system in the 
part of the dorsal mesentery that suspends the developing 
stomach from the body wall. In the adult, the spleen lies 
against the diaphragm, in the area of rib IX to rib X (Fig. 
4.103). It is therefore in the left upper quadrant, or left 
hypochondrium, of the abdomen. 

The spleen is connected to the: 

■ greater curvature of the stomach by the gastrosplenic 
ligament, which contains the short gastric and gastro- 
omental vessels; and 


■ left kidney by the splenorenal ligament (Fig. 4.104), 

which contains the splenic vessels. 

Both these ligaments are parts of the greater omentum. 

The spleen is surrounded by visceral peritoneum except 
in the area of the hilum on the medial surface of the spleen 
(Fig. 4.105). The splenic hilum is the entry point for the 
splenic vessels, and occasionally the tail of the pancreas 
reaches this area. 

The arterial supply to the spleen (Fig. 4.106) is the 
splenic artery from the celiac trunk. 




Stomach 


Lesser omentum 


Splenorenal 

ligament 


Left kidney 

Fig. 4.104 Splenic ligaments and related vasculature. 


Rib IX 

Stomach 

Spleen 


Gastrosplenic 

ligament 


Spleen 

Visceral 

peritoneum 


Descending 

colon 


Greater 

omentum 


Small 

intestine 


Falciform 

ligament 


Liver 


Fig. 4.103 Spleen. 

































Regional anatomy • Abdominal Viscera 



Upper pole 


Hilum 


Visceral surface 


Diaphragmatic 

surface 


Lower pole 


Fig. 4.105 Surfaces and hilum of the spleen. 


Hepatic artery proper Short gastric arteries 



Abdominal aorta 

Posterior superior pancreaticoduodenal artery 
Anterior superior pancreaticoduodenal artery 
Gastroduodenal artery 

Fig. 4.106 Arterial supply to the spleen. 


In the clinic 

Segmental anatomy of the liver 

For many years the segmental anatomy of the liver was of 
little importance. However, since the development of liver 
resection surgery, the size, shape, and segmental anatomy 
of the liver have become clinically important, especially 
with regard to liver resection for metastatic disease. 
Indeed, with detailed knowledge of the segments, 
curative surgery can be performed in patients with tumor 
metastases. 


The liver is divided by the principal plane, which 
divides the organ into halves of approximately equal size. 
This imaginary line is defined by a parasagittal line that 
passes through the gallbladder fossa to the inferior vena 
cava. It is in this plane that the middle hepatic vein is found. 
Importantly, the principal plane divides the left half ofthe 
liver from the right half.The lobes of the liver are unequal in 
size and bear only little relevance to operative anatomy. 

(continues) 

















Abdomen 


In the clinic—cont'd 


The traditional eight-segment anatomy of the liver 
relates to the hepatic arterial, portal, and biliary drainage 
of these segments (Fig. 4.107). 

The caudate lobe is defined as segment I, and the 
remaining segments are numbered in a clockwise fashion 
up to segment VIII. The features are extremely consistent 
between individuals. 


From a surgical perspective, a right hepatectomy 
would involve division of the liver in the principal plane in 
which segments V, VI, VII, and VIII would be removed, 
leaving segments I, II, III, and IV. 


Posterior medial segment VIII (Anterior superior area) 
Medial segment IV (Medial superior area) 



Lateral segment II 
(Lateral superior area) 


Posterior lateral segment VII 
(Posterior superior area)- 


Anterior medial segment V 
(Anterior inferior area) 


Right anterior lateral segment VI 
(Posterior inferior area) 


Anterior medial segment V 
(Anterior inferior area) 


Posterior lateral segment VII 
(Posterior superior area) 


- Caudate process 

Posterior (caudal) segment I— Right caudate lobe 

Left caudate lobe 


— Left anterior lateral segment I 
(Lateral inferior area) 


Lateral segment II 
(Lateral superior area) 


Fig. 4.107 Division of the liver into segments based upon the distributions of the bile ducts and hepatic vessels (Couinaud’s segments). 


340 



















Regional anatomy • Abdominal Viscera 


In the clinic 

Gallstones 

Gallstones are present in approximately 10% of people 
over the age of 40 and are more common in women. They 
consist of a variety of components but are predominantly 
a mixture of cholesterol and bile pigment. They may 
undergo calcification, which can be demonstrated on 
plain radiographs. Gallstones may be visualized 
incidentally as part of a routine abdominal ultrasound 
scan (Fig. 4.108) or on a plain radiograph. 

From time to time, gallstones impact in the region of 
Hartmann's pouch, which is a bulbous region of the neck 
of the gallbladder. When the gallstone lodges in this area, 
the gallbladder cannot empty normally and contractions 
of the gallbladder wall produce severe pain. If this persists, 
a cholecystectomy (removal of the gallbladder) may be 
necessary. 

Sometimes the gallbladder may become inflamed 
(cholecystitis). If the inflammation involves the related 
parietal peritoneum of the diaphragm, pain may not only 
occur in the right upper quadrant of the abdomen but 
may also be referred to the shoulder on the right side. 

This referred pain is due to the innervation of the visceral 
peritoneum of the diaphragm by spinal cord levels (C3 to 
C5) that also innervate skin over the shoulder. In this case, 
one somatic sensory region of low sensory output 
(diaphragm) is referred to another somatic sensory region 
of high sensory output (dermatomes). 


Gallbladder 



Gallstones 


Fig. 4.108 Gallbladder containing multiple stones. Ultrasound 
scan. 

From time to time, small gallstones pass into the bile 
duct and are trapped in the region of the sphincter of the 
ampulla, which obstructs the flow of bile into the 
duodenum. This, in turn, produces jaundice. 


In the clinic 

Jaundice 

Jaundice is a yellow discoloration of the skin caused by 
excess bile pigment (bilirubin) within the plasma. The 
yellow color is best appreciated by looking at the normally 
white sclerae of the eyes, which turn yellow. 

The extent of the elevation of the bile pigments and 
the duration for which they have been elevated account 
for the severity of jaundice. 

Simplified explanation to understanding the types of 
jaundice and their anatomical causes 

When red blood cells are destroyed by the 
reticuloendothelial system, the iron from the hemoglobin 
molecule is recycled, whereas the porphyrin ring (globin) 
compounds are broken down to form fat-soluble bilirubin. 
On reaching the liver via the bloodstream, the fat-soluble 
bilirubin is converted to a water-soluble form of bilirubin. 
This water-soluble bilirubin is secreted into the biliary tree 
and then in turn into the bowel, where it forms the dark 
color of the stool. 


Prehepatic jaundice 

This type of jaundice is usually produced by conditions 
where there is an excessive breakdown of red blood cells 
(e.g., in incompatible blood transfusion and hemolytic 
anemia). 

Hepatic jaundice 

The complex biochemical reactions for converting 
fat-soluble into water-soluble bilirubin may be affected by 
inflammatory change within the liver (e.g., from hepatitis 
or chronic liver disease, such as liver cirrhosis) and poisons 
(e.g., paracetamol overdose). 

Post hepatic jaundice 

Any obstruction of the biliary tree can produce jaundice, 
but the two most common causes are gallstones within 
the bile duct and an obstructing tumor at the head of the 
pancreas. 




Abdomen 


In the clinic 


Spleen disorders 

From a clinical point of view, there are two main 
categories of spleen disorders: rupture and enlargement. 

Splenic rupture 

This tends to occur when there is localized trauma to the 
left upper quadrant. It may be associated with left lower 
rib fractures. Because the spleen has such an extremely 
thin capsule, it is susceptible to injury even when there is 
no damage to surrounding structures, and because the 
spleen is highly vascular, when ruptured, it bleeds 
profusely into the peritoneal cavity. Splenic rupture 
should always be suspected with blunt abdominal injury. 
Current treatments preserve as much of the spleen as 
possible, but some patients require splenectomy. 

Splenic enlargement 

The spleen is an organ of the reticuloendothelial system. 
Diseases that affect the reticuloendothelial system (e.g., 
leukemia, lymphoma, and certain infections) may produce 
generalized lymphadenopathy and enlargement of the 
spleen (splenomegaly) (Fig. 4.109). 


Liver Spleen 



Fig. 4.109 Coronal CT of the abdomen containing a massively 
enlarged spleen (splenomegaly). 


342 





Regional anatomy • Abdominal Viscera 


Arterial supply 

The abdominal aorta begins at the aortic hiatus of the 
diaphragm, anterior to the lower border of vertebra TXII 
(Fig. 4.110). It descends through the abdomen, anterior to 
the vertebral bodies, and by the time it ends at the level of 
vertebra LIV it is slightly to the left of midline. The terminal 
branches of the abdominal aorta are the two common 
iliac arteries. 


Anterior branches of the abdominal aorta 

The abdominal aorta has anterior, lateral, and posterior 
branches as it passes through the abdominal cavity. 
The three anterior branches supply the gastrointestinal 
viscera: the celiac trunk and the superior mesenteric 
and inferior mesenteric arteries (Fig. 4.110). 

The primitive gut tube can be divided into foregut, 
midgut, and hindgut regions. The boundaries of these 


Anterior branches 

Celiac trunk 

Superior mesenteric artery 


Inferior mesenteric artery 



Aortic hiatus 


Diaphragm 


Abdominal aorta 
Psoas major muscle 

Left common iliac artery 


Fig. 4.110 Anterior branches of the abdominal aorta. 





















Abdomen 


regions are directly related to the areas of distribution 
of the three anterior branches of the abdominal aorta 
(Fig. 4.111). 

■ The foregut begins with the abdominal esophagus 
and ends just inferior to the major duodenal papilla, 
midway along the descending part of the duodenum. 
It includes the abdominal esophagus, stomach, 


Foregut 


Midgut 


Hindgut 


Superior mesenteric artery 
Celiac trunk 



Abdominal 

aorta 


Inferior mesenteric artery 


Fig. 4.111 Divisions of the gastrointestinal tract into foregut, 
midgut, and hindgut, summarizing the primary arterial supply to 
each segment. 


duodenum (superior to the major papilla), liver, pan¬ 
creas, and gallbladder. The spleen also develops in rela¬ 
tion to the foregut region. The foregut is supplied by the 
celiac trunk. 

■ The midgut begins just inferior to the major duodenal 
papilla, in the descending part of the duodenum, and 
ends at the junction between the proximal two-thirds 
and distal one-third of the transverse colon. It includes 
the duodenum (inferior to the major duodenal papilla), 
jejunum, ileum, cecum, appendix, ascending colon, and 
right two-thirds of the transverse colon. The midgut is 
supplied by the superior mesenteric artery (Fig. 4.11 1). 

■ The hindgut begins just before the left colic flexure (the 
junction between the proximal two-thirds and distal 
one-third of the transverse colon) and ends midway 
through the anal canal. It includes the left one-third of 
the transverse colon, descending colon, sigmoid colon, 
rectum, and upper part of the anal canal. The hindgut 
is supplied by the inferior mesenteric artery (Fig. 4.111). 


Celiac trunk 

The celiac trunk is the anterior branch of the abdominal 
aorta supplying the fore gut. It arises from the abdominal 
aorta immediately below the aortic hiatus of the dia¬ 
phragm (Fig. 4.112), anterior to the upper part of vertebra 
LI. It immediately divides into the left gastric, splenic, and 
common hepatic arteries. 

Left gastric artery 

The left gastric artery is the smallest branch of the celiac 
trunk. It ascends to the cardioesophageal junction and 
sends esophageal branches upward to the abdominal 
part of the esophagus (Fig. 4.112). Some of these branches 
continue through the esophageal hiatus of the diaphragm 
and anastomose with esophageal branches from the tho¬ 
racic aorta. The left gastric artery itself turns to the right 
and descends along the lesser curvature of the stomach 
in the lesser omentum. It supplies both surfaces of the 
stomach in this area and anastomoses with the right 
gastric artery. 


344 












Regional anatomy • Abdominal Viscera 


Common hepatic artery 


Hepatic artery proper Esophageal branches 


Left hepatic artery 
Right hepatic artery 


Left gastric artery 


Gastroduodenal artery 


Right gastric artery 


Superior pancreaticoduodenal arteries 
A 


Hepatic artery proper 


Gastroduodenal artery 



Short gastric arteries 


Left gastro-omental artery 
Splenic artery 

Right gastro-omental artery 


Left gastro-omental artery 


Splenic artery 


Right gastro-omental artery \ Celiac artery 

Fig. 4.112 Celiac trunk. A. Distribution of the celiac trunk. B. Digital subtraction angiography of the celiac trunk and its branches. 




















Abdomen 


Splenic artery 

The splenic artery, the largest branch of the celiac trunk, 
takes a tortuous course to the left along the superior border 
of the pancreas (Fig. 4.112). It travels in the splenorenal 
ligament and divides into numerous branches, which enter 
the hilum of the spleen. As the splenic artery passes along 
the superior border of the pancreas, it gives off numerous 
small branches to supply the neck, body, and tail of the 
pancreas (Fig. 4.113). 


Approaching the spleen, the splenic artery gives off 
short gastric arteries, which pass through the gastro- 
splenic ligament to supply the fundus of the stomach. It 
also gives off the left gastro-omental artery, which runs 
to the right along the greater curvature of the stomach, 
and anastomoses with the right gastro-omental artery. 



Hepatic artery proper 


Gastroduodenal artery 

Posterior superior 
pancreaticoduodenal artery 

Right gastro-omental artery 


Anterior inferior 
pancreaticoduodenal artery 


Duodenum 


Splenic artery 
Pancreas 
Inferior pancreaticoduodenal artery 


Spleen 


Anterior superior 
pancreaticoduodenal artery 


Left gastro-omental 
artery 


Right gastric artery 
Common hepatic artery 


Short gastric arteries 
Left gastric artery 
Celiac trunk 


Posterior inferior 
pancreaticoduodenal artery 


Superior mesenteric artery 


Fig. 4.113 Arterial supply to the pancreas. 


346 

















Regional anatomy • Abdominal Viscera 



Common hepatic artery 

The common hepatic artery is a medium-sized branch 
of the celiac trunk that runs to the right and divides into 
its two terminal branches, the hepatic artery proper and 
the gastroduodenal artery (Figs. 4.112 and 4.113). 

The hepatic artery proper ascends toward the liver in 
the free edge of the lesser omentum. It runs to the left of 
the bile duct and anterior to the portal vein, and divides 
into the right and left hepatic arteries near the porta 
hepatis (Fig. 4.114). 

As the right hepatic artery nears the liver, it gives off the 
cystic artery to the gallbladder. 

The gastroduodenal artery may give off the supraduo¬ 
denal artery and does give off the posterior superior pan¬ 
creaticoduodenal artery near the upper border of the 
superior part of the duodenum. After these branches the 
gastroduodenal artery continues descending posterior 


to the superior part of the duodenum. Reaching the 
lower border of the superior part of the duodenum, the 
gastroduodenal artery divides into its terminal branches, 
the right gastro-omental artery and the anterior 
superior pancreaticoduodenal artery (Fig. 4.113). 

The right gastro-omental artery passes to the left, 
along the greater curvature of the stomach, eventually 
anastomosing with the left gastro-omental artery from the 
splenic artery. The right gastro-omental artery sends 
branches to both surfaces of the stomach and additional 
branches descend into the greater omentum. 

The anterior superior pancreaticoduodenal artery 
descends and, along with the posterior superior pancreati¬ 
coduodenal artery, supplies the head of the pancreas and 
the duodenum (Fig. 4.11 3). These vessels eventually anas¬ 
tomose with the anterior and posterior branches of the 
inferior pancreaticoduodenal artery. 



Duodenum 


Cystic duct 
Bile duct 


Supraduodenal artery 


Stomach 


Left gastric artery 


Celiac trunk 
Splenic artery 
Right gastric artery 


Left hepatic artery 
Hepatic artery proper 
Portal vein 

Gastroduodenal artery 
Common hepatic artery 


Cystic artery 


Gallbladder 


Right hepatic artery 

Common hepatic duct 


Fig. 4.114 Distribution of the common hepatic artery. 


347 





















Abdomen 


Superior mesenteric artery 

The superior mesenteric artery is the anterior branch 
of the abdominal aorta supplying the midgut. It arises from 
the abdominal aorta immediately below the celiac artery 
(Fig. 4.115), anterior to the lower part of vertebra LI. 

The superior mesenteric artery is crossed anteriorly 
by the splenic vein and the neck of the pancreas. Posterior 
to the artery are the left renal vein, the uncinate process of 
the pancreas, and the inferior part of the duodenum. After 
giving off its first branch (the inferior pancreaticoduo¬ 
denal artery), the superior mesenteric artery gives off 
jejunal and ileal arteries on its left (Fig. 4.11 5). Branch¬ 
ing from the right side of the main trunk of the superior 


mesenteric artery are three vessels—the middle colic, 
right colic, and ileocolic arteries —which supply the 
terminal ileum, cecum, ascending colon, and two-thirds of 
the transverse colon. 

Inferior pancreaticoduodenal artery 

The inferior pancreaticoduodenal artery is the first branch 
of the superior mesenteric artery. It divides immediately 
into anterior and posterior branches, which ascend on the 
corresponding sides of the head of the pancreas. Superi¬ 
orly, these arteries anastomose with anterior and posterior 
superior pancreaticoduodenal arteries (see Figs. 4.114 and 
4.115). This arterial network supplies the head and unci¬ 
nate process of the pancreas and the duodenum. 


Celiac trunk 


Superior mesenteric vein 



Gastroduodenal artery 


Portal vein 


Aortic hiatus 

Pancreas 


Posterior superior 
pancreaticoduodenal artery 


Splenic vein 


Anterior superior 
pancreaticoduodenal artery 

Pancreas 


Posterior inferior 
pancreaticoduodenal artery 


Middle colic artery 


Right gastro-omental artery 


Superior mesenteric artery 
Inferior pancreaticoduodenal artery 


Jejunal arteries 


Duodenum 


Anterior inferior 
pancreaticoduodenal artery 


Fig. 4.115 Initial branching and relationships of the superior mesenteric artery. 


348 
















Regional anatomy • Abdominal Viscera 



Jejunal and ileal arteries 

Distal to the inferior pancreaticoduodenal artery, the 
superior mesenteric artery gives off numerous branches. 
Arising on the left is a large number of jejunal and 
ileal arteries supplying the jejunum and most of the ileum 
(Fig. 4.116). These branches leave the main trunk of the 


artery, pass between two layers of the mesentery, and form 
anastomosing arches or arcades as they pass outward to 
supply the small intestine. The number of arterial arcades 
increases distally along the gut. 

There may be single and then double arcades in the area 
of the jejunum, with a continued increase in the number 



Distal small arteries 


Ileal arteries 


Transverse colon 


Jejunum 


Right colic artery 


Ascending colon 


Ileocolic artery 


Jejunal arteries 


Vasa recta 


Middle colic artery 


Inferior pancreaticoduodenal artery 
Superior mesenteric artery 


Anterior cecal artery 


Posterior cecal artery 
A 


Appendix 

Appendicular artery 


Right colic artery 

Jejunal arteries 


Ileum 

Ileal arteries 


Ileocolic artery 


Fig. 4.116 Superior mesenteric artery. A. Distribution of the superior mesenteric artery. B. Digital subtraction angiography of the superior 
mesenteric artery and its branches. 


349 





































350 


Abdomen 


of arcades moving into and through the area of the ileum. 
Extending from the terminal arcade are vasa recta (straight 
arteries), which provide the final direct vascular supply to 
the walls of the small intestine. The vasa recta supplying 
the jejunum are usually long and close together, forming 
narrow windows visible in the mesentery. The vasa recta 
supplying the ileum are generally short and far apart, 
forming low broad windows. 

Middle colic artery 

The middle colic artery is the first of the three branches 
from the right side of the main trunk of the superior mes¬ 
enteric artery (Fig. 4.116). Arising as the superior mesen¬ 
teric artery emerges from beneath the pancreas, the middle 
colic artery enters the transverse mesocolon and divides 
into right and left branches. The right branch anastomoses 
with the right colic artery while the left branch anastomo¬ 
ses with the lef t colic artery, which is a branch of the infe¬ 
rior mesenteric artery. 

Right colic artery 

Continuing distally along the main trunk of the superior 
mesenteric artery, the right colic artery is the second of the 
three branches from the right side of the main trunk of the 
superior mesenteric artery (Fig. 4.115). It is an inconsis¬ 
tent branch, and passes to the right in a retroperitoneal 
position to supply the ascending colon. Nearing the colon, 
it divides into a descending branch, which anastomoses 
with the ileocolic artery, and an ascending branch, which 
anastomoses with the middle colic artery. 

Ileocolic artery 

The final branch arising from the right side of the superior 
mesenteric artery is the ileocolic artery (Fig. 4.116). This 
passes downward and to the right toward the right iliac 
fossa where it divides into superior and inferior branches: 

■ The superior branch passes upward along the ascending 
colon to anastomose with the right colic artery. 

■ The inferior branch continues toward the ileocolic junc¬ 
tion, dividing into colic, cecal, appendicular, and 
ileal branches (Fig. 4.116). 

The specific pattern of distribution and origin of these 
branches is variable: 

■ The colic branch crosses to the ascending colon and 
passes upward to supply the first part of the ascending 
colon. 

■ Anterior and posterior cecal branches, arising either as 
a common trunk or as separate branches, supply cor¬ 
responding sides of the cecum. 


■ The appendicular branch enters the free margin of and 
supplies the mesoappendix and the appendix. 

■ The ileal branch passes to the left and ascends to supply 
the final part of the ileum before anastomosing with the 
superior mesenteric artery. 

Inferior mesenteric artery 

The inferior mesenteric artery is the anterior branch of the 
abdominal aorta that supplies the hindgut. It is the small¬ 
est of the three anterior branches of the abdominal aorta 
and arises anterior to the body of vertebra LIII. Initially, the 
inferior mesenteric artery descends anteriorly to the aorta 
and then passes to the left as it continues inferiorly (Fig. 
4.11 7). Its branches include the left colic artery, several 
sigmoid arteries, and the superior rectal artery. 

Left colic artery 

The left colic artery is the first branch of the inferior mes¬ 
enteric artery (Fig. 4.117). It ascends retroperitoneally, 
dividing into ascending and descending branches: 

■ The ascending branch passes anteriorly to the left 
kidney, then enters the transverse mesocolon, and 
passes superiorly to supply the upper part of the descend¬ 
ing colon and the distal part of the transverse colon; it 
anastomoses with branches of the middle colic artery. 

■ The descending branch passes inferiorly, supplying the 
lower part of the descending colon, and anastomoses 
with the first sigmoid artery. 

Sigmoid arteries 

The sigmoid arteries consist of two to four branches, which 
descend to the left, in the sigmoid mesocolon, to supply the 
lowest part of the descending colon and the sigmoid colon 
(Fig. 4.117). These branches anastomose superiorly with 
branches from the left colic artery and inferiorly with 
branches from the superior rectal artery. 

Superior rectal artery 

The terminal branch of the inferior mesenteric artery 
is the superior rectal artery (Fig. 4.117). This vessel 
descends into the pelvic cavity in the sigmoid mesocolon, 
crossing the left common iliac vessels. Opposite vertebra 
Sill, the superior rectal artery divides. The two terminal 
branches descend on each side of the rectum, dividing into 
smaller branches in the wall of the rectum. These smaller 
branches continue inferiorly to the level of the internal 
anal sphincter, anastomosing along the way with branches 
from the middle rectal arteries (from the internal iliac 
artery) and the inferior rectal arteries (from the internal 
pudendal artery). 


Regional anatomy • Abdominal Viscera 



Duodenum 

Inferior mesenteric artery 

Superior rectal 
artery 


-Transverse colon 

Descending colon 


Ascending branch, 
of left colic artery 


Descending branch 
of left colic artery 


Left colic artery 


Abdominal aorta 


Sigmoid arteries 

Sigmoid colon 


Rectum 


Superior rectal artery Left colic artery 

Inferior mesenteric artery 



Sigmoid arteries 


Fig. 4.117 Inferior mesenteric artery. A. Distribution of the inferior mesenteric artery. B. Digital subtraction angiography of the inferior 
mesenteric artery and its branches. 


In the clinic 

Vascular supply to the gastrointestinal system 

The abdominal parts of the gastrointestinal system are 
supplied mainly by the celiac trunk and the superior 
mesenteric and inferior mesenteric arteries (Fig. 4.1 18): 

■ The celiac trunk supplies the lower esophagus, 
stomach, superior part of the duodenum, and 
proximal half of the descending part of the 
duodenum. 

■ The superior mesenteric artery supplies the rest of 
the duodenum, the jejunum, the ileum, the 
ascending colon, and the proximal two-thirds of the 
transverse colon. 

■ The inferior mesenteric artery supplies the rest of the 
transverse colon, the descending colon, the sigmoid 
colon, and most of the rectum. 


Along the descending part of the duodenum there is a 
potential watershed area between the celiac trunk blood 
supply and the superior mesenteric arterial blood supply. 

It is unusual for this area to become ischemic, whereas the 
watershed area between the superior mesenteric artery 
and the inferior mesenteric artery, at the splenic flexure, is 
extremely vulnerable to ischemia. 

In certain disease states, the region of the splenic 
flexure of the colon can become ischemic. When this 
occurs, the mucosa sloughs off, rendering the patient 
susceptible to infection and perforation of the large 
bowel, which then requires urgent surgical attention. 

Arteriosclerosis may occur throughout the abdominal 
aorta and at the openings of the celiac trunk and the 
superior mesenteric and inferior mesenteric arteries. Not 

(continues) 
























Abdomen 


In the clinic—cont'd 



Sigmoid arteries 


Celiac trunk 
Common hepatic artery 
Right gastric artery 
Gastroduodenal artery 
Supraduodenal artery 
Duodenum 

Posterior pancreaticoduodenal artery 
Superior mesenteric artery 
Anterior pancreaticoduodenal artery 
Inferior pancreaticoduodenal 


Marginal artery 
Marginal artery 

Inferior mesenteric artery 


Marginal artery 


Left colic artery 


Left gastro-omental artery 

Stomach 
Right gastro-omental artery 


Transverse colon 


Abdominal aorta 


Middle colic artery 
Right colic artery 


Appendicular artery 

Appendix 

Rectum 


Sigmoid colon 
Superior rectal artery 


Esophageal artery 
Left gastric artery 


Short gastric arteries 
Splenic artery 


Left hepatic artery 
Right hepatic artery 
Cystic artery 
Hepatic artery 


Spleen 


Ileocolic artery 
Ascending colon 


Descending colon 


Fig. 4.118 Arterial supply to the abdominal parts of the gastrointestinal system and to the spleen. 


352 





































Regional anatomy • Abdominal Viscera 


In the clinic—cont'd 


infrequently, the inferior mesenteric artery becomes 
occluded. Interestingly, many of these patients do not 
suffer any complications, because anastomoses between 
the right, middle, and left colic arteries gradually enlarge, 
forming a continuous marginal artery. The distal large 
bowel therefore becomes supplied by this enlarged 
marginal artery (marginal artery of Drummond), which 
replaces the blood supply of the inferior mesenteric artery 
(Fig. 4.119). 

If the openings of the celiac trunk and superior 
mesenteric artery become narrowed, the blood supply to 
the gut is diminished. After a heavy meal, the oxygen 
demand of the bowel therefore outstrips the limited 
supply of blood through the stenosed vessels, resulting in 
severe pain and discomfort (mesenteric angina). Patients 
with this condition tend not to eat because of the pain 
and rapidly lose weight. The diagnosis is determined by 
aortic angiography, and the stenoses of the celiac trunk 
and superior mesenteric artery are best appreciated in the 
lateral view. 


Superior mesenteric artery 



Fig. 4.119 Enlarged marginal artery connecting the superior and 
inferior mesenteric arteries. Digital subtraction angiogram. 








Abdomen 


Venous drainage 

Venous drainage of the spleen, pancreas, gallbladder, and 
abdominal part of the gastrointestinal tract, except for the 
inferior part of the rectum, is through the portal system of 
veins, which deliver blood from these structures to the liver. 
Once blood passes through the hepatic sinusoids, it passes 
through progressively larger veins until it enters the hepatic 
veins, which return the venous blood to the inferior vena 
cava just inferior to the diaphragm. 


Ascending toward the liver, the portal vein passes pos¬ 
terior to the superior part of the duodenum and enters the 
right margin of the lesser omentum. As it passes through 
this part of the lesser omentum, it is anterior to the omental 
foramen and posterior to both the bile duct, which is 
slightly to its right, and the hepatic artery proper, which is 
slightly to its left (see Fig. 4.114, p. 347). 

On approaching the liver, the portal vein divides into 
right and left branches, which enter the liver paren¬ 
chyma. Tributaries to the portal vein include: 


Portal vein 

The portal vein is the final common pathway for the 
transport of venous blood from the spleen, pancreas, gall¬ 
bladder, and abdominal part of the gastrointestinal tract. 
It is formed by the union of the splenic vein and the 
superior mesenteric vein posterior to the neck of the 
pancreas at the level of vertebra LII (Fig. 4.120). 


■ right and left gastric veins draining the lesser curva¬ 
ture of the stomach and abdominal esophagus, 

■ cystic veins from the gallbladder, and 

■ the para-umbilical veins, which are associated with 
the obliterated umbilical vein and connect to veins on 
the anterior abdominal wall (Fig. 4.122 on p. 357). 



Pancreas 

Superior mesenteric vein 

Middle colic vein 
Right colic vein 


Ileocolic vein 


Splenic vein 


Inferior mesenteric vein 


Jejunal and ileal veins 


Liver 


Left gastric vein 


Spleen 


Portal vein 


354 


Fig. 4.120 Portal vein. 

















Regional anatomy • Abdominal Viscera 



Splenic vein 

The splenic vein forms from numerous smaller vessels 
leaving the hilum of the spleen (Fig. 4.12 1). It passes to the 
right, passing through the splenorenal ligament with the 
splenic artery and the tail of the pancreas. Continuing 
to the right, the large, straight splenic vein is in contact 
with the body of the pancreas as it crosses the posterior 
abdominal wall. Posterior to the neck of the pancreas, the 
splenic vein joins the superior mesenteric vein to form the 
portal vein. 

Tributaries to the splenic vein include: 

■ short gastric veins from the fundus and left part of the 
greater curvature of the stomach, 


■ the left gastro-omental vein from the greater curva¬ 
ture of the stomach, 

■ pancreatic veins draining the body and tail of the 
pancreas, and 

■ usually the inferior mesenteric vein. 


Superior mesenteric vein 

The superior mesenteric vein drains blood from the small 
intestine, cecum, ascending colon, and transverse colon 
(Fig. 4.12 1). It begins in the right iliac fossa as veins drain¬ 
ing the terminal ileum, cecum, and appendix join, and 
ascends in the mesentery to the right of the superior 
mesenteric artery. 



Spleen 


Portal vein 


Left gastric vein 

Left gastro-omental vein 
Splenic vein 


Liver 


Stomach 

Short gastric veins 


Superior mesenteric vein 
Ascending colon 
Ileum 


Inferior mesenteric vein 
Descending colon 


Sigmoid colon 


Rectum 


Fig. 4.121 Venous drainage of the abdominal portion of the gastrointestinal tract. 


355 























Abdomen 


Posterior to the neck of the pancreas, the superior mes¬ 
enteric vein joins the splenic vein to form the portal vein. 

As a corresponding vein accompanies each branch of 
the superior mesenteric artery, tributaries to the superior 
mesenteric vein include jejunal, ileal, ileocolic, right colic, 
and middle colic veins. Additional tributaries include: 

■ the right gastro-omental vein, draining the right 
part of the greater curvature of the stomach, and 

■ the anterior and posterior inferior pancreatico¬ 
duodenal veins, which pass alongside the arteries of 
the same name; the anterior superior pancreaticoduo¬ 
denal vein usually empties into the right gastro-omental 
vein, and the posterior superior pancreaticoduodenal 
vein usually empties directly into the portal vein. 


Inferior mesenteric vein 

The inferior mesenteric vein drains blood from the 
rectum, sigmoid colon, descending colon, and splenic 
flexure (Fig. 4.12 1). It begins as the superior rectal vein 
and ascends, receiving tributaries from the sigmoid veins 
and the left colic vein. All these veins accompany arteries 
of the same name. Continuing to ascend, the inferior mes¬ 
enteric vein passes posterior to the body of the pancreas 
and usually joins the splenic vein. Occasionally, it ends at 
the junction of the splenic and superior mesenteric veins 
or joins the superior mesenteric vein. 


In the clinic 
Hepatic cirrhosis 

Cirrhosis is a complex disorder of the liver, the diagnosis 
of which is confirmed histologically. When a diagnosis is 
suspected, a liver biopsy is necessary. 

Cirrhosis is characterized by widespread hepatic 
fibrosis interspersed with areas of nodular regeneration 
and abnormal reconstruction of preexisting lobular 
architecture. The presence of cirrhosis implies previous or 
continuing liver cell damage. 

The etiology of cirrhosis is complex and includes toxins 
(alcohol), viral inflammation, biliary obstruction, vascular 
outlet obstruction, nutritional (malnutrition) causes, and 
inherited anatomical and metabolic disorders. 

As the cirrhosis progresses, the intrahepatic vasculature 
is distorted, which in turn leads to increased pressure in 
the portal vein and its draining tributaries (portal 
hypertension). Portal hypertension produces increased 
pressure in the splenic venules, leading to splenic 
enlargement. At the sites of portosystemic anastomosis 
(see below), large dilated veins (varices) develop. These 
veins are susceptible to bleeding and may produce 
marked blood loss, which in some instances can 
be fatal. 

The liver is responsible for the production of numerous 
proteins, including those of the clotting cascade. Any 
disorder of the liver (including infection and cirrhosis) may 
decrease the production of these proteins and so prevent 
adequate blood clotting. Patients with severe cirrhosis of 


the liver have a significant risk of serious bleeding, even 
from small cuts; in addition, when varices rupture, there is 
a danger of rapid exsanguination. 

As the liver progressively fails, the patient develops 
salt and water retention, which produces skin and 
subcutaneous edema. Fluid (ascites) is also retained in the 
peritoneal cavity, which can hold many liters. 

The poorly functioning liver cells (hepatocytes) are 
unable to break down blood and blood products, leading 
to an increase in the serum bilirubin level, which manifests 
as jaundice. 

With the failure of normal liver metabolism, toxic 
metabolic by-products do not convert to nontoxic 
metabolites. This buildup of noxious compounds is made 
worse by the numerous portosystemic shunts, which 
allow the toxic metabolites to bypass the liver. Patients 
may develop severe neurological features, which may lead 
to epileptic fits, dementia, and irreversible neurological 
damage. 

Portosystemic anastomosis 

The hepatic portal system drains blood from the visceral 
organs of the abdomen to the liver. In normal individuals, 

100% of the portal venous blood flow can be recovered 
from the hepatic veins, whereas in patients with elevated 
portal vein pressure (e.g., from cirrhosis), there is 
significantly less blood flow to the liver. The rest of the 
blood enters collateral channels, which drain into the 


356 



Regional anatomy • Abdominal Viscera 


In the clinic—cont'd 

systemic circulation at specific points (Fig. 4.122). The 
largest of these collaterals occur at: 

■ the gastroesophageal junction around the cardia of 
the stomach—where the left gastric vein and its 
tributaries form a portosystemic anastomosis with 
tributaries to the azygos system of veins of the caval 
system; 

■ the anus—the superior rectal vein of the portal 
system anastomoses with the middle and inferior 
rectal veins of the systemic venous system; and 

■ the anterior abdominal wall around the umbilicus— 
the para-umbilical veins anastomose with veins 

on the anterior abdominal wall. 


When the pressure in the portal vein is elevated, 
venous enlargement (varices) tend to occur at and around 
the sites of portosystemic anastomoses and these 
enlarged veins are called: 

■ varices at the anorectal junction, 

■ esophageal varices at the gastroesophageal junction, 
and 

■ caput medusae at the umbilicus. 

Esophageal varices are susceptible to trauma and, once 
damaged, may bleed profusely, requiring urgent surgical 
intervention. 



Rectum 


Tributaries to azygos vein 
Stomach 


Spleen 


Left gastric vein 
Splenic vein 


Inferior mesenteric vein 
Superior mesenteric vein 


Inferior vena cava 


Superior rectal vein 


Liver 


Common iliac vein - 

Internal iliac vein 
External iliac vein 

Inferior rectal veins 


Portal vein 


Para-umbilical veins 
that accompany the 
ligamentum teres 


Superficial veins — 
on abdominal wall 


Fig. 4.122 Portosystemic anastomoses. 




















Abdomen 


Lymphatics 

Lymphatic drainage of the abdominal part of the gastroin¬ 
testinal tract, as low as the inferior part of the rectum, as 
well as the spleen, pancreas, gallbladder, and liver, is 
through vessels and nodes that eventually end in large col¬ 
lections of pre-aortic lymph nodes at the origins of the 
three anterior branches of the abdominal aorta, which 
supply these structures. These collections are therefore 
referred to as the celiac, superior mesenteric, and infe¬ 
rior mesenteric groups of pre-aortic lymph nodes. Lymph 
from viscera is supplied by three routes: 

■ The celiac trunk (i.e., structures that are part of the 
abdominal foregut) drains to pre-aortic nodes near the 
origin of the celiac trunk (Fig. 4.123) —these celiac 
nodes also receive lymph from the superior mesenteric 
and inferior mesenteric groups of pre-aortic nodes, and 
lymph from the celiac nodes enters the cisterna chyli. 

■ The superior mesenteric artery (i.e., structures that are 
part of the abdominal midgut) drains to pre-aortic 
nodes near the origin of the superior mesenteric artery 
(Fig. 4.123) —these superior mesenteric nodes also 
receive lymph from the inferior mesenteric groups of 
pre-aortic nodes, and lymph from the superior mesen¬ 
teric nodes drains to the celiac nodes. 

■ The inferior mesenteric artery (i.e., structures that are 
part of the abdominal hindgut) drains to pre-aortic 
nodes near the origin of the inferior mesenteric artery 
(Fig. 4.123), and lymph from the inferior mesenteric 
nodes drains to the superior mesenteric nodes. 


Innervation 

Abdominal viscera are innervated by both extrinsic and 
intrinsic components of the nervous system: 

■ Extrinsic innervation involves receiving motor impulses 
from, and sending sensory information to, the central 
nervous system. 

■ Intrinsic innervation involves the regulation of digestive 
tract activities by a generally self-sufficient network of 
sensory and motor neurons (the enteric nervous 
system). 

Abdominal viscera receiving extrinsic innervation 
include the abdominal part of the gastrointestinal tract, 
the spleen, the pancreas, the gallbladder, and the liver. 
These viscera send sensory information back to the central 
nervous system through visceral afferent fibers and receive 
motor impulses from the central nervous system through 
358 visceral efferent fibers. 


Celiac nodes 


Diaphragm 

Right kidney 


Superior mesenteric nodes 

Left kidney 


Inferior vena cava Aorta Inferior mesenteric nodes 

Fig. 4.123 Lymphatic drainage of the abdominal portion of the 
gastrointestinal tract. 


The visceral efferent fibers are part of the sympathetic 
and parasympathetic parts of the autonomic division of 
the peripheral nervous system. 

Structural components serving as conduits for these 
afferent and efferent fibers include posterior and anterior 
roots of the spinal cord, respectively, spinal nerves, anterior 
rami, white and gray rami communicantes, the sympa¬ 
thetic trunks, splanchnic nerves carrying sympathetic 
fibers (thoracic, lumbar, and sacral), parasympathetic 
fibers (pelvic), the prevertebral plexus and related ganglia, 
and the vagus nerves [X]. 

The enteric nervous system consists of motor and 
sensory neurons in two interconnected plexuses in the walls 
of the gastrointestinal tract. These neurons control the 
coordinated contraction and relaxation of intestinal smooth 
muscle and regulate gastric secretion and blood flow. 



























Regional anatomy • Abdominal Viscera 


Sympathetic trunks 

The sympathetic trunks are two parallel nerve cords 
extending on either side of the vertebral column from the 
base of the skull to the coccyx (Fig. 4.124). As they pass 
through the neck, they lie posterior to the carotid sheath. 
In the upper thorax, they are anterior to the necks of 
the ribs, while in the lower thorax they are on the lateral 



Fig. 4.124 Sympathetic trunks. 


aspect of the vertebral bodies. In the abdomen, they are 
anterolateral to the lumbar vertebral bodies and, continu¬ 
ing into the pelvis, they are anterior to the sacrum. The two 
sympathetic trunks come together anterior to the coccyx 
to form the ganglion impar. 

Throughout the extent of the sympathetic trunks, small 
raised areas are visible. These collections of neuronal cell 
bodies outside the CNS are the paravertebral sympathetic 
ganglia. There are usually: 

three ganglia in the cervical region, 

eleven or twelve ganglia in the thoracic region, 

four ganglia in the lumbar region, 

four or five ganglia in the sacral region, and 

the ganglion impar anterior to the coccyx (Fig. 4.124). 

The ganglia and trunks are connected to adjacent spinal 
nerves by gray rami communicantes throughout the 
length of the sympathetic trunk and by white rami com¬ 
municantes in the thoracic and upper lumbar parts of the 
trunk (T1 to L2). Neuronal fibers found in the sympathetic 
trunks include preganglionic and postganglionic sym¬ 
pathetic fibers and visceral afferent fibers. 

Splanchnic nerves 

The splanchnic nerves are important components in the 
innervation of the abdominal viscera. They pass from the 
sympathetic trunk or sympathetic ganglia associated with 
the trunk, to the prevertebral plexus and ganglia anterior 
to the abdominal aorta. 

There are two different types of splanchnic nerves, 
depending on the type of visceral efferent fiber they are 
carrying: 

The thoracic, lumbar, and sacral splanchnic nerves 
carry preganglionic sympathetic fibers from the sympa¬ 
thetic trunk to ganglia in the prevertebral plexus, and 
also visceral afferent fibers. 

The pelvic splanchnic nerves (parasympathetic root) 
carry preganglionic parasympathetic fibers from ante¬ 
rior rami of S2, S3, and S4 spinal nerves to an extension 
of the prevertebral plexus in the pelvis (the inferior 
hypogastric plexus or pelvic plexus). 

Thoracic splanchnic nerves 

Three thoracic splanchnic nerves pass from sympa¬ 
thetic ganglia along the sympathetic trunk in the thorax 
to the prevertebral plexus and ganglia associated with the 
abdominal aorta in the abdomen (Fig. 4.125): 

The greater splanchnic nerve arises from the fifth to the 
ninth (or tenth) thoracic ganglia and travels to the 359 


















Abdomen 



Inferior 

hypogastric 

plexus 


Sacral splanchnic nerves 
Pelvic splanchnic nerves 


— Sacral ganglia 

Ganglion impar 


Cervical ganglia 


Thoracic ganglia 


Lumbar ganglia 


Greater splanchnic nerve 
Lesser splanchnic nerve - 
Least splanchnic nerve 


Prevertebral plexus 

Lumbar 
splanchnic nerves 


Thoracic 

splanchnic nerves 


Fig. 4.125 Splanchnic nerves. 











































Regional anatomy • Abdominal Viscera 


celiac ganglion in the abdomen (a prevertebral ganglion 
associated with the celiac trunk). 

■ The lesser splanchnic nerve arises from the ninth and 
tenth (or tenth and eleventh) thoracic ganglia and 
travels to the aorticorenal ganglion. 

■ The least splanchnic nerve, when present, arises from 
the twelfth thoracic ganglion and travels to the renal 
plexus. 

Lumbar and sacral splanchnic nerves 

There are usually two to four lumbar splanchnic nerves, 
which pass from the lumbar part of the sympathetic trunk 
or associated ganglia and enter the prevertebral plexus 
(Fig. 4.125). 

Similarly, the sacral splanchnic nerves pass from the 
sacral part of the sympathetic trunk or associated ganglia 
and enter the inferior hypogastric plexus, which is an 
extension of the prevertebral plexus into the pelvis. 

Pelvic splanchnic nerves 

The pelvic splanchnic nerves (parasympathetic root) 

are unique. They are the only splanchnic nerves that carry 
parasympathetic fibers. In other words, they do not origi¬ 
nate from the sympathetic trunks. Rather, they originate 
directly from the anterior rami of S 2 to S4. Preganglionic 
parasympathetic fibers originating in the sacral spinal cord 
pass from the S2 to S4 spinal nerves to the inferior hypo¬ 
gastric plexus (Fig. 4.125). Once in this plexus, some of 
these fibers pass upward, enter the abdominal prevertebral 
plexus, and distribute with the arteries supplying the 
hindgut. This provides the pathway for innervation of the 
distal one-third of the transverse colon, the descending 
colon, and the sigmoid colon by preganglionic parasympa¬ 
thetic fibers. 

Abdominal prevertebral plexus and ganglia 

The abdominal prevertebral plexus is a collection of nerve 
fibers that surrounds the abdominal aorta and is continu¬ 
ous onto its major branches. Scattered throughout the 
length of the abdominal prevertebral plexus are cell bodies 
of postganglionic sympathetic fibers. Some of these cell 
bodies are organized into distinct ganglia, while others are 
more random in their distribution. The ganglia are usually 
associated with specific branches of the abdominal aorta 
and named after these branches. 

The three major divisions of the abdominal prevertebral 
plexus and associated ganglia are the celiac, aortic, and 
superior hypogastric plexuses (Fig. 4.126). 


■ The celiac plexus is the large accumulation of nerve 
fibers and ganglia associated with the roots of the celiac 
trunk and superior mesenteric artery immediately 
below the aortic hiatus of the diaphragm. Ganglia asso¬ 
ciated with the celiac plexus include two celiac ganglia, 
a single superior mesenteric ganglion, and two aorti¬ 
corenal ganglia. 

■ The aortic plexus consists of nerve fibers and associated 
ganglia on the anterior and lateral surfaces of the 
abdominal aorta extending from just below the origin 
of the superior mesenteric artery to the bifurcation of 
the aorta into the two common iliac arteries. The major 
ganglion in this plexus is the inferior mesenteric gan¬ 
glion at the root of the inferior mesenteric artery. 

■ The superior hypogastric plexus contains numerous 
small ganglia and is the final part of the abdominal pre¬ 
vertebral plexus before the prevertebral plexus contin¬ 
ues into the pelvic cavity. 

Each of these major plexuses gives origin to a number 
of secondary plexuses, which may also contain small 
ganglia. These plexuses are usually named after the vessels 
with which they are associated. For example, the celiac 
plexus is usually described as giving origin to the superior 
mesenteric plexus and the renal plexus, as well as other 
plexuses that extend out along the various branches of the 
celiac trunk. Similarly, the aortic plexus has secondary 
plexuses consisting of the inferior mesenteric plexus, the 
spermatic plexus, and the external iliac plexus. 

Interiorly, the superior hypogastric plexus divides into 
the hypogastric nerves, which descend into the pelvis 
and contribute to the formation of the inferior hypogastric 
or pelvic plexus (Fig. 4.126). 

The abdominal prevertebral plexus receives: 

■ preganglionic parasympathetic and visceral afferent 
fibers from the vagus nerves [X], 

■ preganglionic sympathetic and visceral afferent fibers 
from the thoracic and lumbar splanchnic nerves, and 

■ preganglionic parasympathetic fibers from the pelvic 
splanchnic nerves. 

Parasympathetic innervation 

Parasympathetic innervation of the abdominal part of the 
gastrointestinal tract and of the spleen, pancreas, gallblad¬ 
der, and liver is from two sources—the vagus nerves [X] 
and the pelvic splanchnic nerves. 


Abdomen 


Prevertebral 

plexuses 


Celiac 

plexus 


Aortic 

plexus 


Superior 

hypogastric 

plexus 


Celiac ganglion 



Aorticorenal ganglion 


Superior mesenteric 
ganglion 


Inferior mesenteric 
ganglion 


Hypogastric nerve 


Inferior hypogastric 
plexus 


Fig. 4.126 Abdominal prevertebral plexus and ganglia. 


362 


































Regional anatomy • Abdominal Viscera 



Vagus nerves 

The vagus nerves [X] enter the abdomen associated with 
the esophagus as the esophagus passes through the dia¬ 
phragm (Fig. 4.127) and provide parasympathetic inner¬ 
vation to the foregut and midgut. 

After entering the abdomen as the anterior and poste¬ 
rior vagal trunks, they send branches to the abdominal 
prevertebral plexus. These branches contain preganglionic 
parasympathetic fibers and visceral afferent fibers, which 


are distributed with the other components of the preverte¬ 
bral plexus along the branches of the abdominal aorta. 

Pelvic splanchnic nerves 

The pelvic splanchnic nerves, carrying preganglionic 
parasympathetic fibers from S2 to S4 spinal cord levels, 
enter the inferior hypogastric plexus in the pelvis. Some of 
these fibers move upward into the inferior mesenteric part 
of the prevertebral plexus in the abdomen (Fig. 4.127). 
Once there, these fibers are distributed with branches of 



Pelvic splanchnic nerves 


Esophagus 


Anterior and posterior vagal trunks 


Celiac trunk 

Superior mesenteric artery 


Inferior mesenteric artery 


Fig. 4.127 Parasympathetic innervation of the abdominal portion of the gastrointestinal tract. 


363 



















Abdomen 


the inferior mesenteric artery and provide parasympa¬ 
thetic innervation to the hindgut. 

Enteric system 

The enteric system is a division of the visceral part of the 
nervous system and is a local neuronal circuit in the wall 
of the gastrointestinal tract. It consists of motor and 
sensory neurons organized into two interconnected plex¬ 
uses (the myenteric and submucosal plexuses) between 
the layers of the gastrointestinal wall, and the associated 
nerve fibers that pass between the plexuses and from the 
plexuses to the adjacent tissue (Fig. 4.128). 

The enteric system regulates and coordinates numerous 
gastrointestinal tract activities, including gastric secretory 
activity, gastrointestinal blood flow, and the contraction 
and relaxation cycles of smooth muscle (peristalsis). 

Although the enteric system is generally independent of 
the central nervous system, it does receive input from post¬ 
ganglionic sympathetic and preganglionic parasympa¬ 
thetic neurons that modifies its activities. 

Sympathetic innervation of the stomach 

The pathway of sympathetic innervation of the stomach 
is as follows: 

■ A preganglionic sympathetic fiber originating at the T6 
level of the spinal cord enters an anterior root to leave 
the spinal cord. 


■ At the level of the intervertebral foramen, the anterior 
root (which contains the preganglionic fiber) and a pos¬ 
terior root join to form a spinal nerve. 

■ Outside the vertebral column, the preganglionic fiber 
leaves the anterior ramus of the spinal nerve through 
the white ramus communicans. 

■ The white ramus communicans, containing the pregan¬ 
glionic fiber, connects to the sympathetic trunk. 

■ Entering the sympathetic trunk, the preganglionic fiber 
does not synapse but passes through the trunk and 
enters the greater splanchnic nerve. 

■ The greater splanchnic nerve passes through the crura 
of the diaphragm and enters the celiac ganglion. 

■ In the celiac ganglion, the preganglionic fiber synapses 
with a postganglionic neuron. 

■ The postganglionic fiber joins the plexus of nerve fibers 
surrounding the celiac trunk and continues along its 
branches. 

■ The postganglionic fiber travels through the plexus of 
nerves accompanying the branches of the celiac trunk 
supplying the stomach and eventually reaches its point 
of distribution. 

■ This input from the sympathetic system may modify the 
activities of the gastrointestinal tract controlled by the 
enteric nervous system. 



Mesentery 


Longitudinal muscle layer 


Circular muscle layer 


Mucosal muscle 


Submucosa 


Myenteric plexus 

Submucosal plexus 


Peritoneum 


Fig. 4.128 The enteric system. 


















Regional anatomy • Abdominal Viscera 


In the clinic 
Surgery for obesity 

Surgery for obesity is also known as weight loss surgery 
and bariatric surgery. This type of surgery has become 
increasingly popular over the last few years for patients 
who are unable to achieve significant weight loss through 
appropriate diet modification and exercise programs. It is 
often regarded as a last resort. Importantly, we have to 
recognize the increasing medical impact that overweight 
patients pose. With obesity the patient is more likely to 
develop diabetes and cardiovascular problems and may 
suffer from increased general health disorders. All of 
these have a significant impact on health care budgeting 
and are regarded as serious conditions for the "health 
of a nation." 

There are a number of surgical options to treat obesity. 
Surgery for patients who are morbidly obese can be 
categorized into two main groups: malabsorptive 
procedures and restrictive procedures. 

Malabsorptive procedures 

There are a variety of bypass procedures that produce a 
malabsorption state, preventing further weight gain and 


also producing weight loss. There are complications, 
which may include anemia, osteoporosis, and diarrhea 
(e.g., jejunoileal bypass). 

Predominantly restrictive procedures 
Restrictive procedures involve placing a band or stapling 
in or around the stomach to decrease the size of the 
organ. This reduction produces an earlier feeling of satiety 
and prevents the patient from overeating. 

Combination procedure 

Probably the most popular procedure currently in the 
United States, this procedure involves stapling the 
proximal stomach and joining a loop of small bowel 
to the small gastric remnant. 

Any overweight patient undergoing surgery faces 
significant risk and increased morbidity, with mortality 
rates from 1% to 5%. 


Abdomen 


POSTERIOR ABDOMINAL REGION 

The posterior abdominal region is posterior to the abdomi¬ 
nal part of the gastrointestinal tract, the spleen, and the 
pancreas (Fig. 4.129). This area, bounded by bones and 
muscles making up the posterior abdominal wall, contains 
numerous structures that not only are directly involved in 
the activities of the abdominal contents but also use this 
area as a conduit between body regions. Examples include 


the abdominal aorta and its associated nerve plexuses, the 
inferior vena cava, the sympathetic trunks, and lymphat¬ 
ics. There are also structures originating in this area that 
are critical to the normal function of other regions of the 
body (i.e., the lumbar plexus of nerves), and there are 
organs that associate with this area during development 
and remain in it in the adult (i.e., the kidneys and suprare¬ 
nal glands). 


Inferior vena cava 

Right suprarenal gland 

Right kidney 


Ureter 



Esophagus 
Diaphragm 
Left suprarenal gland 

Left kidney 


Abdominal aorta 
Gonadal vessels 


Bladder 


Fig. 4.129 Posterior abdominal region. 


366 























Regional anatomy • Posterior Abdominal Region 


Posterior abdominal wall 

Bones 

Lumbar vertebrae and the sacrum 

Projecting into the midline of the posterior abdominal area 
are the bodies of the five lumbar vertebrae (Fig. 4.130). 
The prominence of these structures in this region is due to 
the secondary curvature (a forward convexity) of the 
lumbar part of the vertebral column. 



The lumbar vertebrae can be distinguished from cervi¬ 
cal and thoracic vertebrae because of their size. They are 
much larger than any other vertebrae in any other region. 
The vertebral bodies are massive and progressively increase 
in size from vertebra LI to LV. The pedicles are short and 
stocky the transverse processes are long and slender, and 
the spinous processes are large and stubby. The articular 
processes are large and oriented medially and laterally, 
which promotes flexion and extension in this part of the 
vertebral column. 

Between each lumbar vertebra is an intervertebral disc, 
which completes this part of the midline boundary of the 
posterior abdominal wall. 

The midline boundary of the posterior abdominal wall, 
inferior to the lumbar vertebrae, consists of the upper 
margin of the sacrum (Fig. 4.130). The sacrum is formed 
by the fusion of the five sacral vertebrae into a single, 
wedge-shaped bony structure that is broad superiorly and 
narrows inferiorly. Its concave anterior surface and its 
convex posterior surface contain anterior and posterior 
sacral foramina for the anterior and posterior rami of 
spinal nerves to pass through. 

Pelvic bones 

The ilia, which are components of each pelvic bone, attach 
laterally to the sacrum at the sacro-iliac joints (Fig. 4.130). 
The upper part of each ilium expands outward into a thin 
wing-like area (the iliac fossa). The medial side of this 
region of each iliac bone, and the related muscles, are com¬ 
ponents of the posterior abdominal wall. 

Ribs 

Superiorly, ribs XI and XII complete the bony framework of 
the posterior abdominal wall (Fig. 4.130). These ribs are 
unique in that they do not articulate with the sternum or 
other ribs, they have a single articular facet on their heads, 
and they do not have necks or tubercles. 

Rib XI is posterior to the superior part of the left kidney, 
and rib XII is posterior to the superior part of both kidneys. 
Also, rib XII serves as a point of attachment for numerous 
muscles and ligaments. 










Abdomen 


Muscles 

Muscles forming the medial, lateral, inferior, and superior 
boundaries of the posterior abdominal region fill in 
the bony framework of the posterior abdominal wall 
(Table 4.2). Medially are the psoas major and minor 
muscles, laterally is the quadratus lumborum muscle, inte¬ 
riorly is the iliacus muscle, and superiorly is the diaphragm 
(Figs. 4.131 and 4.132). 

Psoas major and minor 

Medially, the psoas major muscles cover the anterolateral 
surface of the bodies of the lumbar vertebrae, filling in the 
space between the vertebral bodies and the transverse pro¬ 
cesses (Fig. 4.131). Each of these muscles arises from the 
bodies of vertebra TXII and all five lumbar vertebrae, from 
the intervertebral discs between each vertebra, and from 
the transverse processes of the lumbar vertebrae. Passing 
inferiorly along the pelvic brim, each muscle continues 
into the anterior thigh, under the inguinal ligament, to 
attach to the lesser trochanter of the femur. 

The psoas major muscle flexes the thigh at the hip joint 
when the trunk is stabilized and flexes the trunk against 
gravity when the body is supine. It is innervated by ante¬ 
rior rami of nerves LI to L3. 

Associated with the psoas major muscle is the psoas 
minor muscle, which is sometimes absent. Lying on the 
surface of the psoas major when present, this slender 
muscle arises from vertebrae TXII and LI and the interven¬ 
ing intervertebral disc; its long tendon inserts into the pec¬ 
tineal line of the pelvic brim and the iliopubic eminence. 


Psoas minor Lumbar vessels 


Psoas major 


Transversus abdominis 



Iliacus 


Quadratus lumborum 


Fig. 4.131 Muscles of the posterior abdominal wall. 


Table4.2 Posterior abdominal wall muscles 


Muscle 

Origin 

Insertion 

Innervation 

Function 

Psoas major 

Lateral surface of bodies of 

TXII and LI to LV vertebrae, 
transverse processes of the 
lumbar vertebrae, and the 
intervertebral discs between 

TXII and LI to LV vertebrae 

Lesser trochanter of the 
femur 

Anterior rami of LI to L3 

Flexion of thigh at hip joint 

Psoas minor 

Lateral surface of bodies of 

TXII and LI vertebrae and 
intervening intervertebral disc 

Pectineal line of the pelvic 
brim and iliopubic 
eminence 

Anterior rami of LI 

Weak flexion of lumbar 
vertebral column 

Quadratus 

lumborum 

Transverse process of LV 
vertebra, iliolumbar ligament, 
and iliac crest 

Transverse processes of LI 
to LIV vertebrae and inferior 
border of rib XII 

Anterior rami of T12 and 

LI to L4 

Depress and stabilize rib 

XII and some lateral 
bending of trunk 

Iliacus 

Upper two-thirds of iliac fossa, 

Lessertrochanter of femur 

Femoral nerve (L2 to L4) 

Flexion ofthigh at hip joint 


anterior sacro-iliac and 
iliolumbar ligaments, and 
upper lateral surface of sacrum 















Regional anatomy • Posterior Abdominal Region 



The psoas minor is a weak flexor of the lumbar vertebral 
column and is innervated by the anterior ramus of 
nerve LI. 

Quadratus lumborum 

Laterally, the quadratus lumborum muscles fill the space 
between rib XII and the iliac crest on both sides of the 
vertebral column (Fig. 4.131). They are overlapped medi¬ 
ally by the psoas major muscles; along their lateral borders 
are the transversus abdominis muscles. 

Each quadratus lumborum muscle arises from the 
transverse process of vertebra LV, the iliolumbar ligament, 
and the adjoining part of the iliac crest. The muscle 
attaches superiorly to the transverse process of the first 
four lumbar vertebrae and the inferior border of rib XII. 

The quadratus lumborum muscles depress and stabilize 
the twelfth ribs and contribute to lateral bending of the 
trunk. Acting together, the muscles may extend the lumbar 
part of the vertebral column. They are innervated by ante¬ 
rior rami of T12 and LI to L4 spinal nerves. 


Iliacus 

Interiorly, an iliacus muscle fills the iliac fossa on each side 
(Fig. 4.131). From this expansive origin covering the iliac 
fossa, the muscle passes inferiorly, joins with the psoas 
major muscle, and attaches to the lesser trochanter of the 
femur. As they pass into the thigh, these combined muscles 
are referred to as the iliopsoas muscle. 

Like the psoas major muscle, the iliacus flexes the thigh 
at the hip joint when the trunk is stabilized and flexes the 
trunk against gravity when the body is supine. It is inner¬ 
vated by branches of the femoral nerve. 

Diaphragm 

Superiorly, the diaphragm forms the boundary of the pos¬ 
terior abdominal region. This musculotendinous sheet also 
separates the abdominal cavity from the thoracic cavity. 

Structurally, the diaphragm consists of a central tendi¬ 
nous part into which the circumferentially arranged 
muscle fibers attach (Fig. 4.132). The diaphragm is 


Inferior phrenic 
artery 



Left phrenic nerve 


Esophagus with anterior 
and posterior vagal trunks 


Greater splanchnic nerve 


Hemi-azygos vein 


Lesser splanchnic nerve 


Thoracic duct 
Aorta 

Right crus 


Least splanchnic nerve 


Left crus 

Sympathetic trunk 


Inferior vena cava 


Right phrenic nerve 


Superior epigastric artery 


Central tendon 


Fig. 4.132 Diaphragm. 


369 














Abdomen 


anchored to the lumbar vertebrae by musculotendinous 
crura, which blend with the anterior longitudinal ligament 
of the vertebral column: 

■ The right crus is the longest and broadest of the crura 
and is attached to the bodies of vertebrae LI to LIII and 
the intervening intervertebral discs (Fig. 4.133). 

■ Similarly, the left crus i s attached t o vertebrae LI and LII 
and the associated intervertebral disc. 


transverse process of vertebra LI and laterally to rib XII 
(Fig. 4.133). 

The medial and lateral arcuate ligaments serve as points 
of origin for some of the muscular components of the 
diaphragm. 

Structures passing through or around the diaphragm 

Numerous structures pass through or around the dia¬ 
phragm (Fig. 4.132): 


The crura are connected across the midline by a tendi¬ 
nous arch (the median arcuate ligament), which passes 
anterior to the aorta (Fig. 4.133). 

Lateral to the crura, a second tendinous arch is formed 
by the fascia covering the upper part of the psoas major 
muscle. This is the medial arcuate ligament, which is 
attached medially to the sides of vertebrae LI and LII 
and laterally to the transverse process of vertebra LI 
(Fig. 4.133). 

A third tendinous arch, the lateral arcuate ligament, 
is formed by a thickening in the fascia that covers the 
quadratus lumborum. It is attached medially to the 


TXII Esophagus Median arcuate 

ligament 



Fig. 4.133 Crura of the diaphragm. 


■ The aorta passes posterior to the diaphragm and ante¬ 
rior to the vertebral bodies at the lower level of vertebra 
TXII; it is between the two crura of the diaphragm and 
posterior to the median arcuate ligament, just to the left 
of midline. 

■ Accompanying the aorta through the aortic hiatus is 
the thoracic duct and, sometimes, the azygos vein. 

■ The esophagus passes through the musculature of the 
right crus of the diaphragm at the level of vertebra TX, 
just to the left of the aortic hiatus. 

■ Passing through the esophageal hiatus with the esopha¬ 
gus are the anterior and posterior vagal trunks, the 
esophageal branches of the left gastric artery and vein, 
and a few lymphatic vessels. 

■ The third large opening in the diaphragm is the caval 
opening, through which the inferior vena cava passes 
from the abdominal cavity to the thoracic cavity (Fig. 
4.132) at approximately vertebra TVIII in the central 
tendinous part of the diaphragm. 

■ Accompanying the inferior vena cava through the caval 
opening is the right phrenic nerve. 

■ The left phrenic nerve passes through the muscular part 
of the diaphragm just anterior to the central tendon on 
the left side. 

Additional structures pass through small openings 

either in or just outside the diaphragm as they pass from 

the thoracic cavity to the abdominal cavity (Fig. 4.132): 

■ The greater, lesser, and least (when present) splanchnic 
nerves pass through the crura, on either side. 

The hemi-azygos vein passes through the left crus. 

■ Passing posterior to the medial arcuate ligament, on 
either side, are the sympathetic trunks. 

■ Passing anterior to the diaphragm, just deep to the ribs, 
are the superior epigastric vessels. 

■ Other vessels and nerves (i.e., the musculophrenic 
vessels and intercostal nerves) also pass through the 
diaphragm at various points. 


370 



















Regional anatomy • Posterior Abdominal Region 


Donnes 

The classic appearance of the right and left domes of the 
diaphragm is caused by the underlying abdominal con¬ 
tents pushing these lateral areas upward, and by the fibrous 
pericardium, which is attached centrally, causing a flatten¬ 
ing of the diaphragm in this area (Fig. 4.134). 

The domes are produced by: 

■ the liver on the right, with some contribution from the 
right kidney and the right suprarenal gland, and 

■ the fundus of the stomach and spleen on the left, with 
contributions from the left kidney and the left suprare¬ 
nal gland. 

Although the height of these domes varies during 
breathing, a reasonable estimate in normal expiration 
places the left dome at the fifth intercostal space and the 
right dome at rib V. This is important to remember when 
percussing the thorax. 

During inspiration, the muscular part of the diaphragm 
contracts, causing the central tendon of the diaphragm to 
be drawn inferiorly. This results in some flattening of the 


Right dome of -Left dome of 

diaphragm diaphragm 





-Heart 


Fig. 4.134 Right and left domes of the diaphragm. Chest 
radiograph. 


domes, enlargement of the thoracic cavity, and a reduction 
in intrathoracic pressure. The physiological effect of these 
changes is that air enters the lungs and venous return to 
the heart is enhanced. 

Blood supply 

There is blood supply to the diaphragm on its superior and 
inferior surfaces: 

■ Superiorly, the musculophrenic and pericardiaco¬ 
phrenic arteries, both branches of the internal thoracic 
artery, and the superior phrenic artery, a branch of the 
thoracic aorta, supply the diaphragm. 

■ Inferiorly, the inferior phrenic arteries, branches of the 
abdominal aorta, supply the diaphragm (see Fig. 4.132). 

Venous drainage is through companion veins to these 
arteries. 

Innervation 

Innervation of the diaphragm is primarily by the phrenic 
nerves. These nerves, from the C3 to C5 spinal cord levels, 
provide all motor innervation to the diaphragm and 
sensory fibers to the central part. They pass through the 
thoracic cavity, between the mediastinal pleura and the 
pericardium, to the superior surface of the diaphragm. At 
this point, the right phrenic nerve accompanies the inferior 
vena cava through the diaphragm and the left phrenic 
nerve passes through the diaphragm by itself (see 
Fig. 4.132). Additional sensory fibers are supplied to the 
peripheral areas of the diaphragm by intercostal nerves. 


In the clinic 
Psoas muscle abscess 

At first glance, it is difficult to appreciate why the psoas 
muscle sheath is of greater importance than any other 
muscle sheath. The psoas muscle and its sheath arise 
not only from the lumbar vertebrae but also from the 
intervertebral discs between each vertebra. This disc 
origin is of critical importance. In certain types of 
infection, the intervertebral disc is preferentially 
affected (e.g., tuberculosis and salmonella discitis). As 
the infection of the disc develops, the infection spreads 
anteriorly and anterolaterally. In the anterolateral 
position, the infection passes into the psoas muscle 
sheath, and spreads within the muscle and sheath, and 
may appear below the inguinal ligament as a mass. 





Abdomen 


In the clinic 

Diaphragmatic hernias 

To understand why a hernia occurs through the 
diaphragm, it is necessary to consider the embryology of 
the diaphragm. 

The diaphragm is formed from four structures—the 
septum transversum, the posterior esophageal mesentery, 
the pleuroperitoneal membrane, and the peripheral 
rim—which eventually fuse together, so separating the 
abdominal cavity from the thoracic cavity. The septum 
transversum forms the central tendon, which develops 
from a mesodermal origin in front of the embryo's head 
and then moves to its more adult position during 
formation of the head fold. 

Fusion of the various components of the diaphragm 
may fail, and hernias may occur through the failed points 
of fusion (Fig. 4.135). The commonest sites are: 

■ between the xiphoid process and the costal margins 
on the right (Morgagni's hernia), and 


■ through an opening on the left when the 
pleuroperitoneal membrane fails to close the 
pericardioperitoneal canal (Bochdalek's hernia). 

Hernias may also occur through the central tendon and 
through a congenitally large esophageal hiatus. 

Morgagni's and Bochdalek's hernias tend to appear at 
or around the time of birth or in early infancy. They allow 
abdominal bowel to enter the thoracic cavity, which may 
compress the lungs and reduce respiratory function. Most 
of these hernias require surgical closure of the 
diaphragmatic defect. 

Occasionally, small defects within the diaphragm fail to 
permit bowel through, but do allow free movement of 
fluid. Patients with ascites may develop pleural effusions, 
while patients with pleural effusions may develop ascites 
when these defects are present. 


Fetal vertebral 
column 


Fetal abdominal 
contents (fluid-filled 
loops of intestine) 
in leftside of 
thoracic cavity 



Fetal diaphragm 
developed on 
right side 


Maternal lumbar 
vertebra 


L Fetal head 


L Normal fetal lung development on right 
side of thoracic cavity 


Fig. 4.135 Fetal diaphragmatic hernia in utero. T2-weighted MR image. Fetus in coronal plane, mother in sagittal plane. 


372 






Regional anatomy • Posterior Abdominal Region 


In the clinic Viscera 

Hiatus hernia Kidneys 


At the level of the esophageal hiatus, the diaphragm 
may be lax, allowing the fundus of the stomach to 
herniate into the posterior mediastinum (Fig. 4.136). 
This typically causes symptoms of acid reflux. Ulceration 
may occur and may produce bleeding and anemia. The 
diagnosis is usually made by barium studies or 
endoscopy. Treatment in the first instance is by medical 
management, although surgery may be necessary. 



The bean-shaped kidneys are retroperitoneal in the poste¬ 
rior abdominal region (Fig. 4.137). They lie in the extra- 
peritoneal connective tissue immediately lateral to the 
vertebral column. In the supine position, the kidneys 
extend from approximately vertebra TXII superiorly to ver¬ 
tebra LIII inferiorly, with the right kidney somewhat lower 
than the left because of its relationship with the liver. 
Although they are similar in size and shape, the left kidney 
is a longer and more slender organ than the right kidney, 
and nearer to the midline. 


Inferior vena cava Esophagus 


Right suprarenal gland 
Diaphragm 


Left suprarenal gland 
Left kidney 



Right kidney 

Abdominal aorta 

— Cut edges of peritoneum — 


Fig. 4.136 Lower esophagus and upper stomach showing a 
hiatus hernia. Radiograph using barium. 


Fig. 4.137 Retroperitoneal position of the kidneys in the 
posterior abdominal region. 


























Abdomen 


Relationships to other structures 

The anterior surface of the right kidney is related to numer¬ 
ous structures, some of which are separated from the 
kidney by a layer of peritoneum and some of which are 
directly against the kidney (Fig. 4.138): 

■ A small part of the superior pole is covered by the right 
suprarenal gland. 

■ Moving inferiorly, a large part of the rest of the upper 
part of the anterior surface is against the liver and is 
separated from it by a layer of peritoneum. 

■ Medially, the descending part of the duodenum is retro¬ 
peritoneal and contacts the kidney. 

■ The inferior pole of the kidney, on its lateral side, is 
directly associated with the right colic flexure and, on 


its medial side, is covered by a segment of the intraperi- 
toneal small intestine. 

The anterior surface of the left kidney is also related 
to numerous structures, some with an intervening layer 
of peritoneum and some directly against the kidney 
(Fig. 4.138): 

■ A small part of the superior pole, on its medial side, is 
covered by the left suprarenal gland. 

■ The rest of the superior pole is covered by the intraperi- 
toneal stomach and spleen. 

■ Moving inferiorly, the retroperitoneal pancreas covers 
the middle part of the kidney. 

■ On its lateral side, the lower half of the kidney is covered 
by the left colic flexure and the beginning of the 



Small intestine 


Descending part 
of duodenum 


Right colic flexure 


Right suprarenal 


Liver 



Descending colon 


Jejunum 


Left suprarenal gland 


Stomach 

Spleen 

Pancreas 

Left colic flexure 


Fig. 4.138 Structures related to the anterior surface of each kidney. 


374 










Regional anatomy • Posterior Abdominal Region 


descending colon, and, on its medial side, by the parts 
of the intraperitoneal jejunum. 

Posteriorly, the right and left kidneys are related to 
similar structures (Fig. 4.139). Superiorly is the diaphragm 
and inferior to this, moving in a medial to lateral direction, 
are the psoas major, quadratus lumborum, and transver- 
sus abdominis muscles. 


The superior pole of the right kidney is anterior to rib 
XII, while the same region of the left kidney is anterior to 
ribs XI and XII. The pleural sacs and specifically, the costo¬ 
diaphragmatic recesses therefore extend posterior to the 
kidneys. 

Also passing posterior to the kidneys are the subcostal 
vessels and nerves and the iliohypogastric and ilio-inguinal 
nerves. 




Rib XI 


Diaphragm 


Rib XII 


Psoas major muscle - 

- Quadratus lumborum muscle 
Transversus abdominis muscle 


Rib XII 


Left kidney 


Right kidney 


Fig. 4.139 Structures related to the posterior surface of each kidney. 
















Abdomen 


Renal fat and fascia 

The kidneys are enclosed in and associated with a unique 
arrangement of fascia and fat. Immediately outside the 
renal capsule, there is an accumulation of extraperitoneal 
fat—the perinephric fat (perirenal fat), which com¬ 
pletely surrounds the kidney (Fig. 4.140). Enclosing the 
perinephric fat is a membranous condensation of the 
extraperitoneal fascia (the renal fascia). The suprarenal 
glands are also enclosed in this fascial compartment, 
usually separated from the kidneys by a thin septum. The 
renal fascia must be incised in any surgical approach to 
this organ. 

At the lateral margins of each kidney, the anterior and 
posterior layers of the renal fascia fuse (Fig. 4.140). This 
fused layer may connect with the transversalis fascia on 
the lateral abdominal wall. 

Above each suprarenal gland, the anterior and posterior 
layers of the renal fascia fuse and blend with the fascia that 
covers the diaphragm. 


Medially, the anterior layer of the renal fascia continues 
over the vessels in the hilum and fuses with the connective 
tissue associated with the abdominal aorta and the inferior 
vena cava (Fig. 4.140). In some cases, the anterior layer 
may cross the midline to the opposite side and blend with 
its companion layer. 

The posterior layer of the renal fascia passes medially 
between the kidney and the fascia covering the quadratus 
lumborum muscle to fuse with the fascia covering the 
psoas major muscle. 

Interiorly, the anterior and posterior layers of the renal 
fascia enclose the ureters. 

In addition to perinephric fat and the renal fascia, a final 
layer of paranephric fat (pararenal fat) completes 
the fat and fascias associated with the kidney (Fig. 4.140). 
This fat accumulates posterior and posterolateral to 
each kidney. 


Anterolateral abdominal 
wall muscles 


Peritoneum 



Renal fascia — 


Paranephric fat 


Transversalis 

fascia 


Quadratus lumborum muscle 


Fig. 4.140 Organization of fat and fascia surrounding the kidney. 


Inferior vena cava 


Psoas major muscle 


376 




























Regional anatomy • Posterior Abdominal Region 


Kidney structure 

Each kidney has a smooth anterior and posterior surface 
covered by a fibrous capsule, which is easily removable 
except during disease. 

On the medial margin of each kidney is the hilum 
of the kidney, which is a deep vertical slit through which 
renal vessels, lymphatics, and nerves enter and leave 
the substance of the kidney (Fig. 4.141). Internally, the 
hilum is continuous with the renal sinus. Perinephric fat 
continues into the hilum and sinus and surrounds all 
structures. 

Each kidney consists of an outer renal cortex and an 
inner renal medulla. The renal cortex is a continuous band 
of pale tissue that completely surrounds the renal medulla. 


Extensions of the renal cortex (the renal columns) project 
into the inner aspect of the kidney, dividing the renal 
medulla into discontinuous aggregations of triangular¬ 
shaped tissue (the renal pyramids). 

The bases of the renal pyramids are directed outward, 
toward the renal cortex, while the apex of each renal 
pyramid projects inward, toward the renal sinus. 
The apical projection (renal papilla) is surrounded by a 
minor calyx. 

The minor calices receive urine and represent the proxi¬ 
mal parts of the tube that will eventually form the ureter 
(Fig. 4.141). In the renal sinus, several minor calices unite 
to form a major calyx, and two or three major calices 
unite to form the renal pelvis, which is the funnel-shaped 
superior end of the ureters. 



Minor calyx 


Hilum of kidney 


Pyramid in renal medulla 


Renal cortex 

Renal papilla 
Renal sinus — 


Renal column 


Renal vein 
Renal pelvis 


Ureter 


Major calyx 


Renal artery 


Fig. 4.141 Internal structure of the kidney. 



















Abdomen 


Renal vasculature and lymphatics 

A single large renal artery, a lateral branch of the abdom¬ 
inal aorta, supplies each kidney. These vessels usually arise 
just inferior to the origin of the superior mesenteric artery 
between vertebrae LI and LII (Fig. 4.142). The left renal 
artery usually arises a little higher than the right, and the 
right renal artery is longer and passes posterior to the 
inferior vena cava. 

As each renal artery approaches the renal hilum, it 
divides into anterior and posterior branches, which supply 
the renal parenchyma. Accessory renal arteries are 
common. They originate from the lateral aspect of the 
abdominal aorta, either above or below the primary renal 


arteries, enter the hilum with the primary arteries or pass 
directly into the kidney at some other level, and are com¬ 
monly called extrahilar arteries. 

Multiple renal veins contribute to the formation of the 
left and right renal veins, both of which are anterior to 
the renal arteries (Fig. 4.142). Importantly, the longer left 
renal vein crosses the midline anterior to the abdominal 
aorta and posterior to the superior mesenteric artery and 
can be compressed by an aneurysm in either of these two 
vessels. 

The lymphatic drainage of each kidney is to the lateral 
aortic (lumbar) nodes around the origin of the renal 
artery. 



Inferior vena cava 


Superior mesenteric artery 


Right renal vein 
Fig. 4.142 Renal vasculature. 


Right kidney 


Right renal artery 


Left renal artery 
Left renal vein 


Abdominal aorta 


Left kidney 


378 



























Regional anatomy • Posterior Abdominal Region 



Ureters 

The ureters are muscular tubes that transport urine from 
the kidneys to the bladder. They are continuous superiorly 
with the renal pelvis, which is a funnel-shaped structure 
in the renal sinus. The renal pelvis is formed from a con¬ 
densation of two or three major calices, which in turn are 
formed by the condensation of several minor calices (see 
Fig. 4.141). The minor calices surround a renal papilla. 


The renal pelvis narrows as it passes inferiorly through 
the hilum of the kidney and becomes continuous with 
the ureter at the ureteropelvic junction (Fig. 4.143). 
Inferior to this junction, the ureters descend retroperitone- 
ally on the medial aspect of the psoas major muscle. At 
the pelvic brim, the ureters cross either the end of the 
common iliac artery or the beginning of the external iliac 
artery, enter the pelvic cavity, and continue their journey 
to the bladder. 


Abdominal aorta 


Right renal artery 


Left renal artery 



First constriction 
—ureteropelvic junction 


Testicular arteries 


External iliac artery 


Third constriction 
—entrance to bladder 


Bladder 


Ureter 


Ureter 


Common iliac artery 


Second constriction 
—pelvic inlet 


Right kidney 


Left kidney 


Fig. 4.143 Ureters. 


379 






























Abdomen 


At three points along their course the ureters are con¬ 
stricted (Fig. 4.143): 

■ The first point is at the ureteropelvic junction. 

■ The second point is where the ureters cross the common 
iliac vessels at the pelvic brim. 

■ The third point is where the ureters enter the wall of the 
bladder. 

Kidney stones can become lodged at these 
constrictions. 

Ureteric vasculature and lymphatics 

The ureters receive arterial branches from adjacent vessels 
as they pass toward the bladder (Fig. 4.143): 

■ The renal arteries supply the upper end. 

■ The middle part may receive branches from the abdomi¬ 
nal aorta, the testicular or ovarian arteries, and the 
common iliac arteries. 

■ In the pelvic cavity, the ureters are supplied by one or 
more arteries from branches of the internal iliac 
arteries. 

In all cases, arteries reaching the ureters divide into 
ascending and descending branches, which form longitu¬ 
dinal anastomoses. 


Lymphatic drainage of the ureters follows a pattern 
similar to that of the arterial supply. Lymph from: 

■ the upper part of each ureter drains to the lateral aortic 
(lumbar) nodes, 

■ the middle part of each ureter drains to lymph nodes 
associated with the common iliac vessels, and 

■ the inferior part of each ureter drains to lymph nodes 
associated with the external and internal iliac vessels. 

Ureteric innervation 

Ureteric innervation is from the renal, aortic, superior 
hypogastric, and inferior hypogastric plexuses through 
nerves that follow the blood vessels. 

Visceral efferent fibers come from both sympathetic and 
parasympathetic sources, whereas visceral afferent fibers 
return to T11 to L2 spinal cord levels. Ureteric pain, which 
is usually related to distention of the ureter, is therefore 
referred to cutaneous areas supplied by Til to L2 spinal 
cord levels. These areas would most likely include the pos¬ 
terior and lateral abdominal wall below the ribs and above 
the iliac crest, the pubic region, the scrotum in males, the 
labia majora in females, and the proximal anterior aspect 
of the thigh. 


In the clinic 

Urinary tract stones 

Urinary tract stones (calculi) occur more frequently in 
men than in women, are most common in people aged 
between 20 and 60 years, and are usually associated 
with sedentary lifestyles. The stones are polycrystalline 
aggregates of calcium, phosphate, oxalate, urate, and 
other soluble salts within an organic matrix. The urine 
becomes saturated with these salts, and small variations in 
the pH cause the salts to precipitate. 

Typically the patient has pain that radiates from the 
infrascapular region (loin) into the groin, and even into 
the scrotum or labia majora. Blood in the urine 
(hematuria) may also be noticed. 

Infection must be excluded because certain species of 
bacteria are commonly associated with urinary tract 
stones. 


The complications of urinary tract stones include 
infection, urinary obstruction, and renal failure. Stones 
may also develop within the bladder and produce marked 
irritation, causing pain and discomfort. 

The diagnosis of urinary tract stones is based upon 
history and examination. Stones are often visible on 
abdominal radiographs. Special investigations include: 

■ ultrasound scanning, which may demonstrate the 
dilated renal pelvis and calices when the urinary 
system is obstructed; and 

■ an intravenous urogram, which will demonstrate the 
obstruction, pinpoint the exact level, and enable the 
surgeon to plan a procedure to remove the stone if 
necessary. 


380 



Regional anatomy • Posterior Abdominal Region 


In the clinic 
Urinary tract cancer 

Most tumors that arise in the kidney are renal cell 
carcinomas. These tumors develop from the proximal 
tubular epithelium. Approximately 5% of tumors within 
the kidney are transitional cell tumors, which arise from 
the urothelium of the renal pelvis. Most patients typically 
have blood in the urine (hematuria), pain in the 
infrascapular region (loin), and a mass. 

Renal cell tumors (Figs. 4.144 and 4.145) are unusual 
because not only do they grow outward from the kidney, 
invading the fat and fascia, but they also spread into the 


renal vein. This venous extension is rare for any other type 
of tumor, so, when seen, renal cell carcinoma should be 
suspected. In addition, the tumor may spread along the 
renal vein and into the inferior vena cava, and in rare 
cases can grow into the right atrium across the tricuspid 
valve and into the pulmonary artery. 

Treatment for most renal cancers is surgical removal, 
even when metastatic spread is present, because some 
patients show regression of metastases. 

Transitional cell carcinoma arises from the urothelium. 
The urothelium is present from the calices to the urethra 



Duodenum 


-Left psoas 

major muscle 


Right renal cancer 


Aorta 

Inferior vena cava 


Left kidney 



Right renal vein Spleen- 


Right kidney tumor 


Aorta 

Inferior vena cava 


Left kidney 


Fig. 4.144 Tumor in the right kidney growing toward, and 
possibly invading, the duodenum. Computed tomogram in the 
axial plane. 


Fig. 4.145 Tumor in the right kidney spreading into the right 
renal vein. Computed tomogram in the axial plane. 


(continues) 


















Abdomen 


In the clinic—cont'd 


and behaves as a "single unit." Therefore, when patients 
develop transitional carcinomas within the bladder, similar 
tumors may also be present within upper parts of the 
urinary tract. In patients with bladder cancer, the whole of 
the urinary tract must always be investigated to exclude 
the possibility of other tumors (Fig. 4.146). 



Fig. 4.146 Transitional cell carcinoma in the pelvis of the right 
kidney. Coronal computed tomogram reconstruction. 


In the clinic 
Nephrostomy 

A nephrostomy is a procedure where a tube is placed 
through the lateral or posterior abdominal wall into the 
renal cortex to lie within the renal pelvis. The function of 
this tube is to allow drainage of urine from the renal pelvis 
through the tube externally (Fig. 4.147). 

The kidneys are situated on the posterior abdominal 
wall, and in thin healthy subjects may be only up to 
2 to 3 cm from the skin. Access to the kidney is relatively 
straightforward, because the kidney can be easily 
visualized under ultrasound guidance. Using local 
anesthetic, a needle can be placed, under ultrasound 


direction, through the skin into the renal cortex and into 
the renal pelvis. A series of wires and tubes can be passed 
through the needle to position the drainage catheter. 

The indications for such a procedure are many. In 
patients with distal ureteric obstruction the back pressure 
of urine within the ureters and the kidney significantly 
impairs the function of the kidney. This will produce renal 
failure and ultimately death. Furthermore, a dilated 
obstructed system is also susceptible to infection. In many 
cases, there is not only obstruction producing renal failure 
but also infected urine within the system. 


382 







Regional anatomy • Posterior Abdominal Region 


In the clinic—cont'd 



“JJ” stent 


Fig. 4.147 This radiograph demonstrates a double-J stent (anteroposterior view). The superior aspect of the double-J stent is situated 
within the renal pelvis. The stent passes through the ureter, describing the path of the ureter, and the tip of the double-J stent is 
projected over the bladder, which appears as a slightly dense area on the radiograph. 


In the clinic 
Kidney transplant 

Kidney transplantation began in the United States in the 
1950s. Since the first transplant, the major problem for 
kidney transplantation has been tissue rejection. A 
number of years have passed since this initial procedure 
and there have been significant breakthroughs in 
transplant rejection medicine. Renal transplantation is 
now a common procedure undertaken in patients with 
end-stage renal failure. 


Transplant kidneys are obtained from either living or 
deceased donors. The living donors are carefully assessed, 
because harvesting a kidney from a normal healthy 
individual, even with modern-day medicine, carries a 
small risk. 

Deceased kidney donors are brain dead or have suffered 
cardiac death. The donor kidney is harvested with a small 
cuff of aortic and venous tissue. The ureter is also harvested. 

(continues) 


Abdomen 


In the clinic—cont'd 

An ideal place to situate the transplant kidney is in the 
left or the right iliac fossa (Fig. 4.148). A curvilinear incision 
is made paralleling the iliac crest and pubic symphysis. 

The external oblique muscle, internal oblique muscle, 
transversus abdominis muscle, and transversalis fascia are 
divided. The surgeon identifies the parietal peritoneum 
but does not enter the peritoneal cavity. The parietal 
peritoneum is medially retracted to reveal the external 
iliac artery, external iliac vein, and bladder. In some 
instances the internal iliac artery of the recipient is 
mobilized and anastomosed directly as an end-to-end 
procedure onto the renal artery of the donor kidney. 
Similarly the internal iliac vein is anastomosed to the 
donor vein. In the presence of a small aortic cuff of tissue 


the donor artery is anastomosed to the recipient external 
iliac artery and similarly for the venous anastomosis. The 
ureter is easily tunneled obliquely through the bladder 
wall with a straightforward anastomosis. 

The left and right iliac fossae are ideal locations for the 
transplant kidney because a new space can be created 
without compromise to other structures. The great 
advantage of this procedure is the proximity to the 
anterior abdominal wall, which permits easy ultrasound 
visualization of the kidney and Doppler vascular 
assessment. Furthermore, in this position biopsies are 
easily obtained. The extra peritoneal approach enables 
patients to make a swift recovery. 


Abdominal aorta- 
Common iliac artery-. 


The left external iliac artery 
has been used to connect 
to the donor kidney 




External iliac -I 
artery 

Internal iliac- 
artery 


Transplant kidney 
in the left iliac 
fossa 



Bladder 


Iliac muscle 
Transplant kidney in left iliac fossa J 


Fig. 4.148 Kidney transplant. A. This image demonstrates an MR angiogram of the bifurcation of the aorta. Attaching to the left 
external iliac artery is the donor artery for a kidney that has been transplanted into the left iliac fossa. B. Abdominal computed 
tomogram, in the axial plane, showing the transplanted kidney in the left iliac fossa. 


384 










Regional anatomy • Posterior Abdominal Region 


In the clinic 


Investigation of the urinary tract 

After an appropriate history and examination of the 
patient, including a digital rectal examination to assess 
the prostate in men, special investigations are required. 

IVU (intravenous urogram) 

An IVU is one of the most important and commonly 
carried out radiological investigations (Fig. 4.149). The 


Spleen 
Left kidney 
Renal pelvis 

Psoas major 
Left ureter 

Bladder 

Right ureter 

Fig. 4.149 Coronal view of 3-D urogram using multidetector 
computed tomography. 


Liver Right kidney 



patient is injected with iodinated contrast medium. Most 
contrast media contain three iodine atoms spaced around 
a benzene ring. The relatively high atomic number of 
iodine compared to the atomic number of carbon, 
hydrogen, and oxygen, attenuates the radiation beam. 
After intravenous injection, contrast media are excreted 
predominantly by glomerular filtration, although some are 
secreted by the renal tubules. This allows visualization of 
the collecting system as well as the ureters and bladder. 

Ultrasound 

Ultrasound can be used to assess kidney size and the size 
of the calices, which may be dilated when obstructed. 
Although the ureters are poorly visualized using 
ultrasound, the bladder can be easily seen when full. 
Ultrasound measurements of bladder volume can be 
obtained before and after micturition. 

Computed tomography 

Computed tomography can be used to assess the kidneys, 
ureters, bladder, and adjacent structures and is a powerful 
tool for staging primary urinary tract tumors. 

Nuclear medicine 

Nuclear medicine is an extremely useful tool for 
investigating the urinary tract because radioisotope 
compounds can be used to estimate renal cell mass and 
function and assess the parenchyma for renal scarring. 
These tests are often very useful in children when renal 
scarring and reflux disease is suspected. 










Abdomen 


Suprarenal glands 

The suprarenal glands are associated with the superior 
pole of each kidney (Fig. 4.150). They consist of an outer 
cortex and an inner medulla. The right gland is shaped like 
a pyramid, whereas the left gland is semilunar in shape and 
the larger of the two. 

Anterior to the right suprarenal gland is part of the 
right lobe of the liver and the inferior vena cava, whereas 


anterior to the left suprarenal gland is part of the stomach, 
pancreas, and, on occasion, the spleen. Parts of the dia¬ 
phragm are posterior to both glands. 

The suprarenal glands are surrounded by the perineph¬ 
ric fat and enclosed in the renal fascia, though a thin 
septum separates each gland from its associated kidney. 


Inferior phrenic arteries 



Right suprarenal gland 


Right kidney 


Superior suprarenal arteries 


Left suprarenal gland 


Inferior vena cava 


Middle 

suprarenal artery 

Inferior 

suprarenal artery 


Left kidney 


Abdominal aorta 


Fig. 4.150 Arterial supply to the suprarenal glands. 


386 
































Regional anatomy • Posterior Abdominal Region 



Suprarenal vasculature 

The arterial supply to the suprarenal glands is extensive 
and arises from three primary sources (Fig. 4.150): 

■ As the bilateral inferior phrenic arteries pass upward 
from the abdominal aorta to the diaphragm, they give 
off multiple branches (superior suprarenal arteries) to 
the suprarenal glands. 

■ A middle branch (middle suprarenal artery) to the 
suprarenal glands usually arises directly from the 
abdominal aorta. 

■ Inferior branches (inferior suprarenal arteries) from the 
renal arteries pass upward to the suprarenal glands. 

In contrast to this multiple arterial supply is the venous 
drainage, which usually consists of a single vein leaving 
the hilum of each gland. On the right side, the right 
suprarenal vein is short and almost immediately enters 
the inferior vena cava, while on the left side, the left supra¬ 
renal vein passes inferiorly to enter the left renal vein. 


Vasculature 

Abdominal aorta 

The abdominal aorta begins at the aortic hiatus of the 
diaphragm as a midline structure at approximately the 
lower level of vertebra TXII (Fig. 4.151). It passes down¬ 
ward on the anterior surface of the bodies of vertebrae LI 
to LIV, ending just to the left of midline at the lower level 
of vertebra LIV. At this point, it divides into the right and 
left common iliac arteries. This bifurcation can be visu¬ 
alized on the anterior abdominal wall as a point approxi¬ 
mately 2.5 cm below the umbilicus or even with a line 
extending between the highest points of the iliac crest. 

As the abdominal aorta passes through the posterior 
abdominal region, the prevertebral plexus of nerves and 
ganglia covers its anterior surface. It is also related to 
numerous other structures: 

■ Anterior to the abdominal aorta, as it descends, are the 
pancreas and splenic vein, the left renal vein, and the 
inferior part of the duodenum. 


Inferior phrenic arteries 


Diaphragm 


Middle suprarenal artery 


Testicular or ovarian arteries 
Lumbar arteries 

Common iliac artery 



Celiac trunk 

Middle suprarenal artery 
Left renal artery 
Superior mesenteric artery 


Inferior mesenteric artery 


Psoas major muscle 
Median sacral artery 


Fig. 4.151 Abdominal aorta. 


387 



























Abdomen 


■ Several lumbar veins cross it posteriorly as they pass to 
the inferior vena cava. 

■ On its right side are the cisterna chyli, thoracic duct, 
azygos vein, right crus of the diaphragm, and the infe¬ 
rior vena cava. 

■ On its left side is the left crus of the diaphragm. 

Branches of the abdominal aorta (Table 4.3) can be 
classified as: 

■ visceral branches supplying organs, 

■ posterior branches supplying the diaphragm or body 
wall, or 

■ terminal branches. 

Visceral branches 

The visceral branches are either unpaired or paired vessels. 

The three unpaired visceral branches that arise from the 
anterior surface of the abdominal aorta (Fig. 4.151) are: 

■ the celiac trunk, which supplies the abdominal foregut, 

■ the superior mesenteric artery, which supplies the 
abdominal midgut, and 

■ the inferior mesenteric artery, which supplies the 
abdominal hindgut. 

The paired visceral branches of the abdominal aorta 
(Fig. 4.151) include: 

■ the middle suprarenal arteries—small, lateral branches 
of the abdominal aorta arising just above the renal 


arteries that are part of the multiple vascular supply to 
the suprarenal gland; 

■ the renal arteries—lateral branches of the abdominal 
aorta that arise just inferior to the origin of the superior 
mesenteric artery between vertebrae LI and LII, and 
supply the kidneys; and 

■ the testicular or ovarian arteries—anterior branches of 
the abdominal aorta that arise below the origin of the 
renal arteries, and pass downward and laterally on the 
anterior surface of the psoas major muscle. 

Posterior branches 

The posterior branches of the abdominal aorta are vessels 
supplying the diaphragm or body wall. They consist of the 
inferior phrenic arteries, the lumbar arteries, and the 
median sacral artery (Fig. 4.151). 

Inferior phrenic arteries 

The inferior phrenic arteries arise immediately 
inferior to the aortic hiatus of the diaphragm either 
directly from the abdominal aorta, as a common trunk 
from the abdominal aorta, or from the base of the celiac 
trunk (Fig. 4.151). Whatever their origin, they pass 
upward, provide some arterial supply to the suprarenal 
gland, and continue onto the inferior surface of the 
diaphragm. 

Lumbar arteries 

There are usually four pairs of lumbar arteries arising 
from the posterior surface of the abdominal aorta 


Table 4.3 Branches of the abdominal aorta 

Artery 

Branch 

Origin 

Parts supplied 

Celiac trunk 

Anterior 

Immediately inferior to the aortic hiatus of 
the diaphragm 

Abdominal foregut 

Superior mesenteric artery 

Anterior 

Immediately inferior to the celiac trunk 

Abdominal midgut 

Inferior mesenteric artery 

Anterior 

Inferior to the renal arteries 

Abdominal hindgut 

Middle suprarenal arteries 

Lateral 

Immediately superior to the renal arteries 

Suprarenal glands 

Renal arteries 

Lateral 

Immediately inferior to the superior 
mesenteric artery 

Kidneys 

Testicular or ovarian arteries 

Paired anterior 

Inferior to the renal arteries 

Testes in male and ovaries in female 

Inferior phrenic arteries 

Lateral 

Immediately inferior to the aortic hiatus 

Diaphragm 

Lumbar arteries 

Posterior 

Usually four pairs 

Posterior abdominal wall and spinal 
cord 

Median sacral artery 

Posterior 

Just superior to the aortic bifurcation, passes 
interiorly across lumbar vertebrae, sacrum, 
and coccyx 


Common iliac arteries 

Terminal 

Bifurcation usually occurs at the level of LIV 
vertebra 



388 



Regional anatomy • Posterior Abdominal Region 



(Fig. 4.151). They run laterally and posteriorly over the 
bodies of the lumbar vertebrae, continue laterally, passing 
posterior to the sympathetic trunks and between the trans¬ 
verse processes of adjacent lumbar vertebrae, and reach 
the abdominal wall. From this point onward, they demon¬ 
strate a branching pattern similar to a posterior intercostal 
artery, which includes providing segmental branches that 
supply the spinal cord. 

In the clinic 

Abdominal aortic stent graft 

An abdominal aortic aneurysm is a dilatation of the aorta 
and generally tends to occur in the infrarenal region (the 
region at or below the renal arteries). As the aorta expands, 
the risk of rupture increases, and it is now generally 
accepted that when an aneurysm reaches 5.5 cm or greater 
an operation will significantly benefit the patient. 

With the aging population, the number of abdominal 
aortic aneurysms is increasing. Moreover, with the 
increasing use of imaging techniques a number of 
abdominal aortic aneurysms are identified in 
asymptomatic patients. 

For many years the standard treatment for repair was 
an open operative technique, which involved a large 
incision from the xiphoid process of the sternum to the 
symphysis pubis and dissection of the aneurysm. The 
aneurysm was excised and a tubular woven graft was 
sewn into place. Recovery may take a number of days, 
even weeks, and most patients would be placed in the 
intensive care unit after the operation. 

Further developments and techniques have led to a 
new type of procedure being performed to treat 



Median sacral artery 

The final posterior branch is the median sacral artery 
(Fig. 4.151). This vessel arises from the posterior surface of 
the abdominal aorta just superior to the bifurcation and 
passes in an inferior direction, first over the anterior surface 
of the lower lumbar vertebrae and then over the anterior 
surface of the sacrum and coccyx. 


abdominal aortic aneurysms—the endovascular graft. The 
idea of placing the graft into the aortic aneurysm and 
lining the dilated vessel is not new and was first described 
over 10 years ago. Since the original description the 
devices have been modified on a number of occasions 
(Fig. 4.152). 

The technique involves surgically dissecting the 
femoral artery below the inguinal ligament. A small 
incision is made in the femoral artery and the preloaded 
compressed graft with metal support struts is passed on a 
large catheter into the abdominal aorta through the 
femoral artery. Using X-ray for guidance the graft is 
opened, lining the inside of the aorta. Limb attachments 
are made to the graft that extend into the common iliac 
vessels. This bifurcated tube device effectively excludes 
the abdominal aortic aneurysm. 

This type of device is not suitable for all patients. 
Patients who receive this device do not need to go to the 
intensive care unit. Many patients leave the hospital 
within 24 to 48 hours. Importantly, this device can be used 
for patients who were deemed unfit for open surgical 
repair. 



Fig. 4.152 Volume-rendered reconstruction using multidetector computed tomography of patient with an infrarenal abdominal aortic 
aneurysm before (A) and after (B) endovascular aneurysm repair. Note the image only demonstrates the intraluminal contrast and not 
the entire vessel. White patches in the aorta represent intramural calcium. 


389 




390 


Abdomen 


Inferior vena cava 

The inferior vena cava returns blood from all structures 
below the diaphragm to the right atrium of the heart. It is 
formed when the two common iliac veins come together at 
the level of vertebra LV, just to the right of midline. It 
ascends through the posterior abdominal region anterior 
to the vertebral column immediately to the right of the 
abdominal aorta (Fig. 4.153), continues in a superior 


direction, and leaves the abdomen by piercing the central 
tendon of the diaphragm at the level of vertebra TVIII. 

During its course, the anterior surface of the inferior 
vena cava is crossed by the right common iliac artery, the 
root of the mesentery, the right testicular or ovarian artery, 
the inferior part of the duodenum, the head of the pan¬ 
creas, the superior part of the duodenum, the bile duct, the 
portal vein, and the liver, which overlaps and on occasion 
completely surrounds the vena cava (Fig. 4.153). 



Inferior phrenic veins 


Right kidney 


Hepatic veins 
Esophagus 

Inferior vena cava 
Left kidney 

Left renal vein 


Right testicular 
or ovarian vein 


Abdominal aorta 


Right external iliac Left external iliac 

artery and vein artery and vein 


Right femoral Left femoral 

artery and vein artery and vein 


Fig. 4.153 Inferior vena cava. 





















Regional anatomy • Posterior Abdominal Region 



Tributaries to the inferior vena cava include the: 

■ common iliac veins, 

■ lumbar veins, 

■ right testicular or ovarian vein, 

■ renal veins, 

■ right suprarenal vein, 

■ inferior phrenic veins, and 

■ hepatic veins. 

There are no tributaries from the abdominal part of the 
gastrointestinal tract, the spleen, the pancreas, or the gall¬ 
bladder, because veins from these structures are compo¬ 
nents of the portal venous system, which first passes 
through the liver. 

Of the venous tributaries mentioned above, the lumbar 
veins are unique in their connections and deserve special 
attention. Not all of the lumbar veins drain directly into the 
inferior vena cava (Fig. 4.154): 

■ The fifth lumbar vein generally drains into the iliolum¬ 
bar vein, a tributary of the common iliac vein. 

■ The third and fourth lumbar veins usually drain into the 
inferior vena cava. 


Azygos vein 


Ascending 
lumbar vein 

Lumbar vein 

Inferior 
vena cava 



Hemi-azygos 

vein 


Left renal vein 

Ascending 
lumbar vein 

Lumbar vein 

Iliolumbar vein 


Common iliac 
vein 


Lateral sacral 
vein 


■ The first and second lumbar veins may empty into the 
ascending lumbar veins. 

The ascending lumbar veins are long, anastomosing 
venous channels that connect the common iliac, iliolum¬ 
bar, and lumbar veins with the azygos and hemi-azygos 
veins of the thorax (Fig. 4.154). 

If the inferior vena cava becomes blocked, the ascend¬ 
ing lumbar veins become important collateral channels 
between the lower and upper parts of the body. 


In the clinic 
Inferior vena cava filter 

Deep vein thrombosis is a potentially fatal condition 
where a clot (thrombus) is formed in the deep venous 
system of the legs and the veins of the pelvis. Virchow 
described the reasons for thrombus formation as 
decreased blood flow, abnormality of the constituents 
of blood, and abnormalities of the vessel wall. Common 
predisposing factors include hospitalization and 
surgery, the oral contraceptive pill, smoking, and air 
travel. Other factors include clotting abnormalities 
(e.g., protein S and protein C deficiency). 

The diagnosis of deep vein thrombosis may be 
difficult to establish, with symptoms including leg 
swelling and pain and discomfort in the calf. It may 
also be an incidental finding. 

In practice, patients with suspected deep vein 
thrombosis undergo a D-dimer blood test, which 
measures levels of a fibrin degradation product. If this 
is positive there is a high association with deep vein 
thrombosis. 

The consequences of deep vein thrombosis are 
twofold. Occasionally the clot may dislodge and pass 
into the venous system through the right side of the 
heart and into the main pulmonary arteries. If the clots 
are of significant size they obstruct blood flow to the 
lung and may produce instantaneous death. Secondary 
complications include destruction of the normal 
valvular system in the legs, which may lead to venous 
incompetency and chronic leg swelling with ulceration. 

The treatment for deep vein thrombosis is 
prevention. In order to prevent deep vein thrombosis, 
patients are optimized by removing all potential risk 
factors. Subcutaneous heparin may be injected and the 
patient wears compression stockings to prevent venous 
stasis while in the hospital. 

In certain situations it is not possible to optimize the 
patient with prophylactic treatment, and it may be 
necessary to insert a filter into the inferior vena cava 
that traps any large clots. It may be removed after the 
risk period has ended. 


Fig. 4.154 Lumbar veins. 


391 













Abdomen 


Lymphatic system 

Lymphatic drainage from most deep structures and regions 
of the body below the diaphragm converges mainly on col¬ 
lections of lymph nodes and vessels associated with the 
major blood vessels of the posterior abdominal region (Fig. 
4.155). The lymph then predominantly drains into the 
thoracic duct. Major lymphatic channels that drain differ¬ 
ent regions of the body as a whole are summarized in 


Table 4.4 (also see Chapter 1, pp. 29-30, for discussion of 
lymphatics in general). 

Pre-aortic and lateral aortic or lumbar nodes 
(para-aortic nodes) 

Approaching the aortic bifurcation, the collections of 
lymphatics associated with the two common iliac arteries 
and veins merge, and multiple groups of lymphatic vessels 
and nodes associated with the abdominal aorta and 



External iliac nodes 


Intestinal trunk 


Cisterna chyli 


Right lumbar trunk with 
lateral aortic (lumbar) nodes 


Inferior vena cava 


Inferior mesenteric nodes 


Celiac nodes 

Superior mesenteric nodes 


Pre-aortic nodes 


Left lumbar trunk with 
lateral aortic (lumbar) nodes 

Common iliac nodes 


External iliac nodes 


Internal iliac nodes 


Fig. 4.155 Abdominal lymphatics. 


Table 4.4 Lymphatic drainage 


Lymphatic vessel 

Right jugular trunk 

Left jugular trunk 

Right subclavian trunk 

Left subclavian trunk 

Right bronchomediastinal trunk 

Left bronchomediastinal trunk 

Thoracic duct 


Area drained 

Right side of head and neck 
Left side of head and neck 

Right upper limb, superficial regions of thoracic and upper abdominal walls 

Left upper limb, superficial regions of thoracic and upper abdominal walls 

Right lung and bronchi, mediastinal structures, thoracic wall 

Left lung and bronchi, mediastinal structures, thoracic wall 

Lower limbs, abdominal walls and viscera, pelvic walls and viscera, thoracic wall 























Regional anatomy • Posterior Abdominal Region 


inferior vena cava pass superiorly. These collections may be 
subdivided into pre-aortic nodes, which are anterior to 
the abdominal aorta, and right and left lateral aortic or 
lumbar nodes (para-aortic nodes), which are posi¬ 
tioned on either side of the abdominal aorta (Fig. 4.155). 

As these collections of lymphatics pass through the pos¬ 
terior abdominal region, they continue to collect lymph 
from a variety of structures. The lateral aortic or lumbar 
lymph nodes (para-aortic nodes) receive lymphatics from 
the body wall, the kidneys, the suprarenal glands, and the 
testes or ovaries. 

The pre-aortic nodes are organized around the three 
anterior branches of the abdominal aorta that supply the 


abdominal part of the gastrointestinal tract, as well as the 
spleen, pancreas, gallbladder, and liver. They are divided 
into celiac, superior mesenteric, and inferior mesenteric 
nodes, and receive lymph from the organs supplied by the 
similarly named arteries. 

Finally, the lateral aortic or lumbar nodes form the right 
and left lumbar trunks, whereas the pre-aortic nodes form 
the intestinal trunk (Fig. 4.155). These trunks come 
together and form a confluence that, at times, appears as 
a saccular dilation (the cisterna chyli). This confluence of 
lymph trunks is posterior to the right side of the abdominal 
aorta and anterior to the bodies of vertebrae LI and LII. It 
marks the beginning of the thoracic duct. 


In the clinic 

Retroperitoneal lymph node surgery 

From a clinical perspective, retroperitoneal lymph nodes 
are arranged in two groups. The pre-aortic lymph node 
group drains lymph from the embryological midline 
structures, such as the liver, bowel, and pancreas. The 
para-aortic lymph node group (the lateral aortic or lumbar 
nodes), on either side of the aorta, drain lymph from 
bilateral structures, such as the kidneys and adrenal 
glands. Organs embryologically derived from the 
posterior abdominal wall also drain lymph to these 
nodes. These organs include the ovaries and the testes 
(importantly, the testes do not drain lymph to the 
inguinal regions). 

In general, lymphatic drainage follows standard 
predictable routes; however, in the presence of disease, 
alternate routes of lymphatic drainage will occur. 

There are a number of causes for enlarged 
retroperitoneal lymph nodes. In the adult, massively 
enlarged lymph nodes are a feature of lymphoma, and 
smaller lymph node enlargement is observed in the 
presence of infection and metastatic malignant spread of 
disease (e.g., colon cancer). 

The treatment for malignant lymph node disease is 
based upon a number of factors, including the site of the 
primary tumor (e.g., bowel) and its histological cell type. 
Normally, the primary tumor is surgically removed and the 
lymph node spread and metastatic organ spread (e.g., to 
the liver and the lungs) are often treated with 
chemotherapy and radiotherapy. 


In certain instances it may be considered appropriate 
to resect the lymph nodes in the retroperitoneum (e.g., for 
testicular cancer). 

The surgical approach to retroperitoneal lymph node 
resection involves a lateral paramedian incision in the 
midclavicular line. The three layers of the anterolateral 
abdominal wall (external oblique, internal oblique, and 
transversus abdominis) are opened and the transversalis 
fascia is divided. The next structure the surgeon sees is 
the parietal peritoneum. Instead of entering the parietal 
peritoneum, which is standard procedure for most 
intraabdominal operations, the surgeon gently pushes the 
parietal peritoneum toward the midline, which moves the 
intraabdominal contents and allows a clear view of the 
retroperitoneal structures. On the left, the para-aortic 
lymph node group is easily demonstrated, with a clear 
view of the abdominal aorta and kidney. On the right the 
inferior vena cava is demonstrated and has to be retracted 
to access the right para-aortic lymph node chain. 

The procedure of retroperitoneal lymph node 
dissection is extremely well tolerated and lacks the 
problems of entering the peritoneal cavity (e.g., paralytic 
ileus). Unfortunately, a complication of a vertical incision 
in the midclavicular line is division of the segmental nerve 
supply to the rectus abdominis muscle. This produces 
muscle atrophy and asymmetrical proportions of the 
anterior abdominal wall. 


Abdomen 


Nervous system in the posterior 
abdominal region 

Several important components of the nervous system are 
in the posterior abdominal region. These include the sym¬ 
pathetic trunks and associated splanchnic nerves, the 
plexus of nerves and ganglia associated with the abdomi¬ 
nal aorta, and the lumbar plexus of nerves. 

Sympathetic trunks and splanchnic nerves 

The sympathetic trunks pass through the posterior abdom¬ 
inal region anterolateral to the lumbar vertebral bodies, 
before continuing across the sacral promontory and into 


the pelvic cavity (Fig. 4.156). Along their course, small 
raised areas are visible. These represent collections of neu¬ 
ronal cell bodies—primarily postganglionic neuronal cell 
bodies—which are located outside the central nervous 
system. They are sympathetic paravertebral ganglia. There 
are usually four ganglia along the sympathetic trunks in 
the posterior abdominal region. 

Also associated with the sympathetic trunks in the pos¬ 
terior abdominal region are the lumbar splanchnic nerves 
(Fig. 4.156). These components of the nervous system pass 
from the sympathetic trunks to the plexus of nerves and 
ganglia associated with the abdominal aorta. Usually two 
to four lumbar splanchnic nerves carry preganglionic sym¬ 
pathetic fibers and visceral afferent fibers. 


Celiac ganglion 


Sympathetic trunk and ganglion 


Lumbar splanchnic nerves 



Superior mesenteric ganglion 


Aorticorenal ganglion 

Lumbar splanchnic nerves 

Sympathetic trunk 
and ganglion 

Inferior mesenteric ganglion 


Hypogastric nerves 


Inferior hypogastric plexus 


Fig. 4.156 Sympathetic trunks passing through the posterior abdominal region. 


394 

















Regional anatomy • Posterior Abdominal Region 


Abdominal prevertebral plexus and ganglia 

The abdominal prevertebral plexus is a network of nerve 
fibers surrounding the abdominal aorta. It extends from 
the aortic hiatus of the diaphragm to the bifurcation of 
the aorta into the right and left common iliac arteries. 
Along its route, it is subdivided into smaller, named plex¬ 
uses (Fig. 4.157): 

■ Beginning at the diaphragm and moving inferiorly, the 
initial accumulation of nerve fibers is referred to as the 


celiac plexus—this subdivision includes nerve fibers 
associated with the roots of the celiac trunk and supe¬ 
rior mesenteric artery. 

■ Continuing inferiorly, the plexus of nerve fibers 
extending from just below the superior mesenteric 
artery to the aortic bifurcation is the abdominal aortic 
plexus (Fig. 4.157). 

■ At the bifurcation of the abdominal aorta, the abdomi¬ 
nal prevertebral plexus continues inferiorly as the supe¬ 
rior hypogastric plexus. 


Prevertebral 

plexus 


Celiac 

plexus 


Aortic 

plexus 


Superior 

hypogastric 

plexus 



Celiac ganglion 

Superior mesenteric ganglion 

Aorticorenal ganglion 

Lumbar splanchnic nerves 
Sympathetic trunk and ganglion 

Inferior mesenteric ganglion 


Hypogastric nerve 


Inferior hypogastric plexus 


Fig. 4.157 Prevertebral plexus and ganglia in the posterior abdominal region. 


















Abdomen 


Throughout its length, the abdominal prevertebral 
plexus is a conduit for: 

■ preganglionic sympathetic and visceral afferent fibers 
from the thoracic and lumbar splanchnic nerves, 

■ preganglionic parasympathetic and visceral afferent 
fibers from the vagus nerves [X], and 

■ preganglionic parasympathetic fibers from the pelvic 
splanchnic nerves (Fig. 4.158). 

Associated with the abdominal prevertebral plexus are 
clumps of nervous tissue (the prevertebral ganglia), 


which are collections of postganglionic sympathetic neu¬ 
ronal cell bodies in recognizable aggregations along the 
abdominal prevertebral plexus; they are usually named 
after the nearest branch of the abdominal aorta. They are 
therefore referred to as celiac, superior mesenteric, 
aorticorenal, and inferior mesenteric ganglia (Fig. 
4.159). These structures, along with the abdominal pre¬ 
vertebral plexus, play a critical role in the innervation of 
the abdominal viscera. 

Common sites for pain referred from the abdominal 
viscera and from the heart are given in Table 4.5. 



Posterior root 


Visceral afferent 


Gray ramus 


Posterior and 
anterior rami 


White ramus 
communicans 


Celiac ganglion 

Preganglionic parasympathetic 


Sympathetic 
ganglion and trunk 


Enteric neuron 


Greater splanchnic nerve 


Anterior root 


Esophagus - 


Vagus nerve 


Aorta 


Preganglionic sympathetic 
Postganglionic sympathetic 


Fig. 4.158 Nerve fibers passing through the abdominal prevertebral plexus and ganglia. 


396 













Regional anatomy • Posterior Abdominal Region 


Celiac ganglion 


Superior mesenteric 
ganglion 


Aorticorenal ganglion 


Inferior mesenteric 
ganglion 


Fig. 4.159 Prevertebral ganglia associated with the prevertebral plexus. 



Table 4.5 Referred pain pathways (visceral afferents) 


Organ 

Afferent pathway 

Spinal cord level 

Referral area 

Heart 

Thoracic splanchnic nerves 

T1 to T4 

Upper thorax and medial arm 

Foregut (organs supplied by celiac 
trunk) 

Greater splanchnic nerve 

T5 to T9 (orTIO) 

Lower thorax and epigastric region 

Midgut (organs supplied by superior 
mesenteric artery) 

Lesser splanchnic nerve 

T9,T10 (or T10, Til) 

Umbilical region 

Kidneys and upper ureter 

Least splanchnic nerve 

T12 

Flanks (lateral regions) 

Hindgut (organs supplied by inferior 
mesenteric artery) and lower ureter 

Lumbar splanchnic nerves 

LI, L2 

Pubic region, lateral and anterior thighs, 
and groin 
















Abdomen 


Lumbar plexus 

The lumbar plexus is formed by the anterior rami of nerves 
LI to L3 and most of the anterior ramus of L4 (Fig. 4.160 
and Table 4.6). It also receives a contribution from the T12 
(subcostal) nerve. 

Branches of the lumbar plexus include the iliohypogas¬ 
tric, ilio-inguinal and genitofemoral nerves lateral cutane¬ 
ous nerve of the thigh (lateral femoral cutaneous) and 
femoral and obturator nerves. The lumbar plexus forms in 
the substance of the psoas major muscle anterior to its 
attachment to the transverse processes of the lumbar ver¬ 
tebrae (Fig. 4.161). Therefore, relative to the psoas major 
muscle, the various branches emerge either: 

■ anterior—genitofemoral nerve, 

■ medial—obturator nerve, or 

■ lateral—iliohypogastric, ilio-inguinal, and femoral 
nerves and the lateral cutaneous nerve of the thigh. 

Iliohypogastric and ilio-inguinal nerves (LI) 

The iliohypogastric and ilio-inguinal nerves arise as a 
single trunk from the anterior ramus of nerve LI (Fig. 
4.160). Either before or soon after emerging from the 
lateral border of the psoas major muscle, this single trunk 
divides into the iliohypogastric and the ilio-inguinal nerves. 



Fig. 4.160 Lumbar plexus. 


Table 4.6 Branches of the lumbar plexus 


Branch 

Origin 

Spinal segments 

Function: motor 

Function: sensory 

Iliohypogastric 

Anterior ramus LI 

LI 

Internal oblique and 
transversus abdominis 

Posterolateral gluteal skin and skin in 
pubic region 

Ilio-inguinal 

Anterior ramus LI 

LI 

Internal oblique and 
transversus abdominis 

Skin in the upper medial thigh, and 
either the skin over the root of the 
penis and anterior scrotum or the 
mons pubis and labium majus 

Genitofemoral 

Anterior rami LI and L2 

LI, L2 

Genital branch—male 
cremasteric muscle 

Genital branch—skin of anterior 
scrotum or skin of mons pubis and 
labium majus; femoral branch—skin of 
upper anterior thigh 

Lateral cutaneous 
nerve of thigh 

Anterior rami L2 and L3 

L2, L3 


Skin on anterior and lateral thigh to 
the knee 

Obturator 

Anterior rami L2 to L4 

L2 to L4 

Obturator externus, pectineus, 
and muscles in medial 
compartment of thigh 

Skin on medial aspect of the thigh 

Femoral 

Anterior rami L2 to L4 

L2 to L4 

lliacus, pectineus, and muscles 
in anterior compartment of 
thigh 

Skin on anterior thigh and medial 
surface of leg 


398 








Regional anatomy • Posterior Abdominal Region 


Subcostal nerve 
Iliohypogastric nerve 

llio-inguinal nerve 

Lateral cutaneous 
nerve of thigh 

Femoral nerve 
Genitofemoral nerve 
Obturator nerve 



Lumbosacral trunks 
(L4,L5) 


Subcostal nerve (T12) 
Psoas major muscle 
Iliohypogastric nerve (LI) 
llio-inguinal nerve (LI) 


Genitofemoral nerve (L1,L2) 

lliacus muscle 

Lateral cutaneous 
nerve of thigh (L2.L3) 

Femoral nerve (L2 to L4) 


Obturator nerve (L2 to L4) 


Fig. 4.161 Lumbar plexus in the posterior abdominal region. 
























Abdomen 


Iliohypogastric nerve 

The iliohypogastric nerve passes across the anterior 
surface of the quadratus lumborum muscle, posterior to 
the kidney. It pierces the transversus abdominis muscle and 
continues anteriorly around the body between the trans¬ 
versus abdominis and internal oblique muscles. Above the 
iliac crest, a lateral cutaneous branch pierces the inter¬ 
nal and external oblique muscles to supply the posterolat¬ 
eral gluteal skin (Fig. 4.162). 

The remaining part of the iliohypogastric nerve (the 
anterior cutaneous branch) continues in an anterior 


direction, piercing the internal oblique just medial to the 
anterior superior iliac spine as it continues in an obliquely 
downward and medial direction. Becoming cutaneous, just 
above the superficial inguinal ring, after piercing the apo¬ 
neurosis of the external oblique, it distributes to the skin 
in the pubic region (Fig. 4.162). Throughout its course, it 
also supplies branches to the abdominal musculature. 

Ilio-inguinal nerve 

The ilio-inguinal nerve is smaller than, and inferior to, the 
iliohypogastric nerve as it crosses the quadratus lumborum 


T12 


Genitofemoral nerve (LI ,L2) 

Ilio-inguinal nerve (LI) 

Lateral cutaneous 
nerve of thigh (L2,L3) 

Obturator nerve (L2 to L4) 


Femoral nerve (L2 to L4) 



T10 

Til 

T12 

Lateral cutaneous branch 
of iliohypogastric nerve (LI) 

Anterior cutaneous branch 
of iliohypogastric nerve (LI) 


Ilio-inguinal nerve (LI) 

Femoral branch of 
genitofemoral nerve (L1,L2) 

Lateral cutaneous 
nerve of thigh (L2,L3) 


Cutaneous branch of 
obturator nerve (L2 to L4) 


Intermediate cutaneous 
from femoral nerve 

Medial cutaneous from 
femoral nerve 


Saphenous nerve from femoral nerve 


400 


Fig. 4.162 Cutaneous distribution of the nerves from the lumbar plexus. 






















































Regional anatomy • Posterior Abdominal Region 


muscle. Its course is more oblique than that of the iliohy¬ 
pogastric nerve, and it usually crosses part of the iliacus 
muscle on its way to the iliac crest. Near the anterior end 
of the iliac crest, it pierces the transversus abdominis 
muscle, and then pierces the internal oblique muscle and 
enters the inguinal canal. 

The ilio-inguinal nerve emerges through the superficial 
inguinal ring, along with the spermatic cord, and provides 
cutaneous innervation to the upper medial thigh, the 
root of the penis, and the anterior surface of the scrotum 
in men, or the mons pubis and labium majus in women 
(Fig. 4.162). Throughout its course, it also supplies 
branches to the abdominal musculature. 

Genitofemoral nerve (LI and L2) 

The genitofemoral nerve arises from the anterior rami of 
nerves LI and L2 (Fig. 4.160). It passes downward in the 
substance of the psoas major muscle until it emerges on 
the anterior surface of the psoas major. It then descends on 
the surface of the muscle, in a retroperitoneal position, 
passing posterior to the ureter. It eventually divides into 
genital and femoral branches. 

The genital branch continues downward and enters 
the inguinal canal through the deep inguinal ring. It con¬ 
tinues through the canal and: 

■ in men, innervates the cremasteric muscle and termi¬ 
nates on the skin in the upper anterior part of the 
scrotum, and 

■ in women, accompanies the round ligament of the 
uterus and terminates on the skin of the mons pubis 
and labium majus. 

The femoral branch descends on the lateral side of the 
external iliac artery and passes posterior to the inguinal 
ligament, entering the femoral sheath lateral to the femoral 
artery. It pierces the anterior layer of the femoral sheath 
and the fascia lata to supply the skin of the upper anterior 
thigh (Fig. 4.162). 

Lateral cutaneous nerve of thigh (L2 and L3) 

The lateral cutaneous nerve of the thigh arises from the 
anterior rami of nerves L2 and L3 (Fig. 4.160). It emerges 
from the lateral border of the psoas major muscle, passing 
obliquely downward across the iliacus muscle toward the 
anterior superior iliac spine (Fig. 4.162). It passes posterior 
to the inguinal ligament and enters the thigh. 

The lateral cutaneous nerve of the thigh supplies the 
skin on the anterior and lateral thigh to the level of the 
knee (Fig. 4.162). 


Obturator nerve (L2 to L4) 

The obturator nerve arises from the anterior rami of nerves 
L2 to L4 (Fig. 4.160). It descends in the psoas major 
muscle, emerging from its medial side near the pelvic brim 
(Fig. 4.161). 

The obturator nerve continues posterior to the common 
iliac vessels, passes across the lateral wall of the pelvic 
cavity, and enters the obturator canal, through which the 
obturator nerve gains access to the medial compartment 
of the thigh. 

In the area of the obturator canal, the obturator nerve 
divides into anterior and posterior branches. On enter¬ 
ing the medial compartment of the thigh, the two branches 
are separated by the obturator externus and adductor 
brevis muscles. Throughout their course through the 
medial compartment, these two branches supply: 

■ articular branches to the hip joint, 

■ muscular branches to the obturator externus, pectin- 
eus, adductor longus, gracilis, adductor brevis, and 
adductor magnus muscles, 

■ cutaneous branches to the medial aspect of the 
thigh, and 

■ in association with the saphenous nerve, cutaneous 
branches to the medial aspect of the upper part of the 
leg and articular branches to the knee joint (Fig. 4.162). 

Femoral nerve (L2 to L4) 

The femoral nerve arises from the anterior rami of nerves 
L2 to L4 (Fig. 4.160). It descends through the substance of 
the psoas major muscle, emerging from the lower lateral 
border of the psoas major (Fig. 4.161). Continuing 
its descent, the femoral nerve lies between the lateral 
border of the psoas major and the anterior surface of the 
iliacus muscle. It is deep to the iliacus fascia and lateral 
to the femoral artery as it passes posterior to the inguinal 
ligament and enters the anterior compartment of the 
thigh. Upon entering the thigh, it immediately divides into 
multiple branches. 

Cutaneous branches of the femoral nerve include: 

■ medial and intermediate cutaneous nerves supplying 
the skin on the anterior surface of the thigh, and 

■ the saphenous nerve supplying the skin on the medial 
surface of the leg (Fig. 4.162). 

Muscular branches innervate the iliacus, pectineus, sar- 
torius, rectus femoris, vastus medialis, vastus intermedius, 
and vastus lateralis muscles. Articular branches supply the 
hip and knee joints. 


Abdomen 


Surface anatomy 


Abdomen surface anatomy 

Visualization of the position of abdominal viscera is funda¬ 
mental to a physical examination. Some of these viscera or 
their parts can be felt by palpating through the abdominal 
wall. Surface features can be used to establish the positions 
of deep structures. 

Defining the surface projection 
of the abdomen 

Palpable landmarks can be used to delineate the extent 
of the abdomen on the surface of the body. These land¬ 
marks are: 

■ the costal margin above and 

■ the pubic tubercle, anterior superior iliac spine, and iliac 
crest below (Fig. 4.163). 


The costal margin is readily palpable and separates the 
abdominal wall from the thoracic wall. 

A line between the anterior superior iliac spine and the 
pubic tubercle marks the position of the inguinal ligament, 
which separates the anterior abdominal wall above from 
the thigh of the lower limb below. 

The iliac crest separates the posterolateral abdominal 
wall from the gluteal region of the lower limb. 

The upper part of the abdominal cavity projects above 
the costal margin to the diaphragm, and therefore abdomi¬ 
nal viscera in this region of the abdomen are protected by 
the thoracic wall. 

The level of the diaphragm varies during the breathing 
cycle. The dome of the diaphragm on the right can reach 
as high as the fourth costal cartilage during forced 
expiration. 


Diaphragm 

Costal margin 

Iliac crest 

Anterior superior iliac spine 

Inguinal ligament 
Pubic tubercle 



Thorax 


Abdomen 


Lower limb 


402 


Fig. 4.163 Interior view of the abdominal region of a man. Palpable bony landmarks, the inguinal ligament, and the position of the 
diaphragm are indicated. 












Surface anatomy • How to Find the Superficial Inguinal Ring 



How to find the superficial inguinal ring 

The superficial inguinal ring is an elongate triangular 
defect in the aponeurosis of the external oblique (Fig. 
4.164). It lies in the lower medial aspect of the anterior 
abdominal wall and is the external opening of the inguinal 


canal. The inguinal canal and superficial ring are larger in 
men than in women: 

■ In men, structures that pass between the abdomen and 
the testis pass through the inguinal canal and superfi¬ 
cial inguinal ring. 


Anterior superior iliac spine 
Inguinal ligament 
Femoral artery 


Spermatic cord 



Aponeurosis of external oblique 

Deep inguinal ring 
Superficial inguinal ring 

Position of pubic symphysis 


Anterior superior iliac spine 
Inguinal ligament 

Femoral artery 

Round ligament of uterus 



Aponeurosis of external oblique 
Deep inguinal ring 
Superficial inguinal ring 
Position of pubic symphysis 



Fig. 4.164 Groin. A. In a man. B. In a woman. C. Examination of the superficial inguinal ring and related regions of the inguinal canal in 
a man. 


403 
































Abdomen 


■ In women, the round ligament of the uterus passes 
through the inguinal canal and superficial inguinal ring 
to merge with connective tissue of the labium majus. 

The superficial inguinal ring is superior to the pubic 
crest and tubercle and to the medial end of the inguinal 
ligament: 

■ In men, the superficial inguinal ring can be easily 
located by following the spermatic cord superiorly to the 
lower abdominal wall—the external spermatic fascia of 
the spermatic cord is continuous with the margins of 
the superficial inguinal ring. 

■ In women, the pubic tubercle can be palpated and the 
ring is superior and lateral to it. 

The deep inguinal ring, which is the internal opening to 
the inguinal canal, lies superior to the inguinal ligament, 
midway between the anterior superior iliac spine and pubic 


symphysis. The pulse of the femoral artery can be felt in 
the same position but below the inguinal ligament. 

Because the superficial inguinal ring is the site where 
inguinal hernias appear, particularly in men, the ring and 
related parts of the inguinal canal are often evaluated 
during physical examination. 

How to determine lumbar vertebral levels 

Lumbar vertebral levels are useful for visualizing the posi¬ 
tions of viscera and major blood vessels. The approximate 
positions of the lumbar vertebrae can be established using 
palpable or visible landmarks (Fig. 4.165): 

■ A horizontal plane passes through the medial ends of 
the ninth costal cartilages and the body of the LI 
vertebra—this transpyloric plane cuts through the body 
midway between the suprasternal (jugular) notch and 
the pubic symphysis. 


Transpyloric plane 

Subcostal plane 

Umbilicus 

Supracristal plane 

Intertubercular plane 










Jugular notch 


End of ninth costal cartilage 

Lower edge of tenth 
costal cartilage 

Highest point on iliac crest 


Tubercle of crest of ilium 


Pubic symphysis 


404 


Fig. 4.165 Landmarks used for establishing the positions of lumbar vertebrae are indicated. Anterior view of the abdominal region of a man. 














Surface anatomy • Visualizing Structures at the LI Vertebral Level 



■ A horizontal plane passes through the lower edge of the 
costal margin (tenth costal cartilage) and the body of 
the LIII vertebra—the umbilicus is normally on a hori¬ 
zontal plane that passes through the disc between the 
LIII and LIV vertebrae. 

■ A horizontal plane (supracristal plane) through the 
highest point on the iliac crest passes through the spine 
and body of the LIV vertebra; 

■ A plane through the tubercles of the crest of the ilium 
passes through the body of the LV vertebra. 

Visualizing structures at the LI 
vertebral level 

The LI vertebral level is marked by the transpyloric plane, 
which cuts transversely through the body midway between 


the jugular notch and pubic symphysis, and through 
the ends of the ninth costal cartilages (Fig. 4.166). At this 
level are: 

■ the beginning and upper limit of the end of the 
duodenum, 

■ the hila of the kidneys, 

■ the neck of the pancreas, and 

■ the origin of the superior mesenteric artery from the 
aorta. 

The left and right colic flexures also are close to this 
level. 


Neck of pancreas 


Duodenum 

Transpyloric plane 


Superior mesenteric artery 



Jugular notch 


End of ninth costal cartilage 


Kidney 


Pubic symphysis 


Fig. 4.166 LI vertebral level and the important viscera associated with this level. Anterior view of the abdominal region of a man. 


405 












Abdomen 


Visualizing the position of major 
blood vessels 

Each of the vertebral levels in the abdomen is related to the 
origin of major blood vessels (Fig. 4.167): 

■ The celiac trunk originates from the aorta at the upper 
border of the LI vertebra. 

■ The superior mesenteric artery originates at the lower 
border of the LI vertebra. 


■ The renal arteries originate at approximately the LII 
vertebra. 

■ The inferior mesenteric artery originates at the LIII 
vertebra. 

■ The aorta bifurcates into the right and left common iliac 
arteries at the level of the LIV vertebra. 

■ The left and right common iliac veins join to form the 
inferior vena cava at the LV vertebral level. 


Inferior vena cava — 

Transpyloric plane — 

Subcostal plane — 
Umbilicus — 
Supracristal plane — 

Intertubercular plane — 



Jugular notch 


Aorta 

Upper border of LI 
Celiac trunk 

Lower border of LI 
Superior mesenteric artery 

LII Approximate origin 
of renal artery 

LIII Inferior mesenteric artery 

LIV Bifurcation of aorta 

LV Joining of common iliac 
veins to form the inferior 
vena cava 

Pubic symphysis 


Fig. 4.167 Major vessels projected onto the body’s surface. Anterior view of the abdominal region of a man. 


406 
















Surface anatomy • Using Abdominal Quadrants to Locate Major Viscera 


Using abdominal quadrants to locate 
major viscera 

The abdomen can be divided into quadrants by a vertical 
median plane and a horizontal transumbilical plane, which 
passes through the umbilicus (Fig. 4.168): 

■ The liver and gallbladder are i n the right upper quadrant. 

■ The stomach and spleen are in the left upper quadrant. 

■ The cecum and appendix are in the right lower quadrant. 

■ The end of the descending colon and sigmoid colon are 
in the left lower quadrant. 


Most of the liver is under the right dome of the dia¬ 
phragm and is deep to the lower thoracic wall. The inferior 
margin of the liver can be palpated descending below the 
right costal margin when a patient is asked to inhale deeply. 
On deep inspiration, the edge of the liver can be felt 
“slipping” under the palpating fingers placed under the 
costal margin. 

A common surface projection of the appendix is 
McBurney’s point, which is one-third of the way up along 
a line from the right anterior superior iliac spine to the 
umbilicus. 


Sagittal plane 


Liver 
Diaphragm 
Costal margin 
Gallbladder 

Transumbilical plane 

McBurney's point 
Anterior superior iliac spine 

Appendix 
Inguinal ligament 
Pubic tubercle 



Spleen 

Stomach 


Descending colon 


Sigmoid colon 


Fig. 4.168 Abdominal quadrants and the positions of major viscera. Anterior view of a man. 
















Abdomen 


Defining surface regions to which pain 
from the gut is referred 

The abdomen can be divided into nine regions by a midcla- 
vicular sagittal plane on each side and by the subcostal 
and intertubercular planes, which pass through the 
body transversely (Fig. 4.169). These planes separate the 
abdomen into: 


■ three central regions (epigastric, umbilical, pubic), and 

■ three regions on each side (hypochondrium, flank, 
groin). 

Pain from the abdominal part of the foregut is referred 
to the epigastric region, pain from the midgut is referred to 
the umbilical region, and pain from the hindgut is referred 
to the pubic region. 


Epigastric region 

-referred pain from foregut 


Umbilical region 

-referred pain from midgut 


Pubic region 

-referred pain from hindgut 



Midclavicular planes 


Subcostal plane 


Intertubercular plane 

Anterior superior iliac spine 
Inguinal ligament 
Pubic tubercle 


Fig. 4.169 The nine regions of the abdomen. Anterior view of a woman. 


408 

















Surface anatomy • Where to Find the Spleen 



Where to find the kidneys 

The kidneys project onto the back on either side of the 
midline and are related to the lower ribs (Fig. 4.170): 

■ The left kidney is a little higher than the right and 
reaches as high as rib XI. 

■ The superior pole of the right kidney reaches only as 
high as rib XII. 

The lower poles of the kidneys occur around the level of 
the disc between the LIII and LIV vertebrae. The hila of the 


kidneys and the beginnings of the ureters are at approxi¬ 
mately the LI vertebra. 

The ureters descend vertically anterior to the tips of the 
transverse processes of the lower lumbar vertebrae and 
enter the pelvis. 

Where to find the spleen 

The spleen projects onto the left side and back in the area 
of ribs IX to XI (Fig. 4.171). The spleen follows the contour 
of rib X and extends from the superior pole of the left 
kidney to just posterior to the midaxillary line. 


Rib XI 


Left kidney 
Left ureter 


Rib XII 

Right kidney 

Transverse processes 
of lumbar vertebrae 


Fig. 4.170 Surface projection of the kidneys 


CHIU UICICI 3. 




Fig. 4.171 Surface projection of the spleen. Posterior view of a man. 


409 











Abdomen 



Clinical cases 


Case 1 

TRAUMATIC RUPTURE OF THE DIAPHRAGM 

A 45-year-old man had mild epigastric pain, and a 
diagnosis of esophageal reflux was made. He was 
given appropriate medication, which worked well. 
However, at the time of the initial consultation, the 
family practitioner requested a chest radiograph, 
which demonstrated a prominent hump on the left 
side of the diaphragm and old rib fractures. 

The patient was recalled for further questioning. 

He was extremely pleased with the treatment he had 
been given for his gastroesophageal reflux, but was 
concerned about being recalled for further history and 
examination. During the interview, he revealed that he 
had previously been involved in a motorcycle accident 
and had undergone a laparotomy for a "rupture." The 
patient did not recall what operation was performed, but 
was assured at the time that the operation was a great 
success. 


The patient is likely to have undergone a splenectomy. 

In any patient who has had severe blunt abdominal 
trauma (such as that caused by a motorcycle accident), 
lower left-sided rib fractures are an extremely important 
sign of appreciable trauma. 

A review of the patient's old notes revealed that at the 
time of the injury the spleen was removed surgically, but 
it was not appreciated that there was a small rupture of 
the dome of the left hemidiaphragm. The patient 
gradually developed a hernia through which bowel could 
enter, producing the "hump" on the diaphragm seen on 
the chest radiograph. 

Because this injury occurred many years ago and the 
patient has been asymptomatic, it is unlikely that the 
patient will come to any harm and was discharged. 


Case 2 

CHRONIC THROMBOSIS OF THE INFERIOR VENA CAVA 

A medical student was asked to inspect the abdomen 
of two patients. On the first patient he noted irregular 
veins radiating from the umbilicus. On the second 
patient he noted irregular veins, coursing in a caudal 
to cranial direction, over the anterior abdominal wall 
from the groin to the chest. He was asked to explain 
his findings and determine the significance of these 
features. 

In the first patient the veins were draining radially away 
from the periumbilical region. In normal individuals, 
enlarged veins do not radiate from the umbilicus. In 
patients with portal hypertension the portal venous 
pressure is increased as a result of hepatic disease. Small 
collateral veins develop at and around the obliterated 
umbilical vein. These veins pass through the umbilicus 
and drain onto the anterior abdominal wall, forming a 
portosystemic anastomosis. The eventual diagnosis for 
this patient was cirrhosis of the liver. 

The finding of veins draining in a caudocranial direction 
on the anterior abdominal wall in the second patient is 


not typical for veins on the anterior abdominal wall. 

When veins are so prominent, it usually implies that there 
is an obstruction to the normal route of venous drainage 
and an alternative route has been taken. Typically, blood 
from the lower limbs and the retroperitoneal organs 
drains into the inferior vena cava and from here to the 
right atrium of the heart. This patient had a chronic 
thrombosis of the inferior vena cava, preventing blood 
from returning to the heart by the "usual" route. 

Blood from the lower limbs and the pelvis may drain via 
a series of collateral vessels, some of which include 
the superficial inferior epigastric veins, which run in the 
superficial fascia. These anastomose with the superior, 
superficial, and deep epigastric venous systems to drain 
into the internal thoracic veins, which in turn drain into 
the brachiocephalic veins and the superior vena cava. 

After the initial inferior vena cava thrombosis, the veins 
of the anterior abdominal wall and other collateral 
pathways hypertrophy to accommodate the increase in 
blood flow. 


410 








Clinical cases • Cose 3 


Case 3 

LIVER BIOPSY IN PATIENTS WITH SUSPECTED 
LIVER CIRRHOSIS 

A 55-year-old man developed severe jaundice and 
a massively distended abdomen. A diagnosis of 
cirrhosis of the liver was made, and further 
confirmatory tests demonstrated that the patient 
had significant ascites (free fluid within the 
peritoneal cavity). A liver biopsy was necessary 
to confirm the cirrhosis, but there was some 
debate about how this biopsy should be obtained 
(Fig. 4.172). 

In patients with cirrhosis it is important to determine the 
extent of the cirrhosis and the etiology. 

History, examination, and blood tests are useful and are 
supported by complex radiological investigations. To 
begin treatment and determine the prognosis, a sample 
of liver tissue must be obtained. However, there are 
important issues to consider when taking a liver biopsy 
from a patient with suspected cirrhosis. 

One issue is liver function. 


Biopsy needle in- 

right hepatic vein 



Fig. 4.172 Transjugular liver biopsy needle in the right hepatic 
vein. Radiograph. 


The liver function of patients with suspected liver disease 
is poor, as demonstrated by the patient's jaundice—an 
inability to conjugate bilirubin. Importantly, because 
some liver products are blood-clotting factors involved in 
the clotting cascade, the blood-clotting ability of patients 
with severe liver disease is significantly impaired. These 
patients therefore have a high risk of bleeding. 

Another issue is the presence of ascites. 

Normally the liver rests against the lateral and anterior 
abdominal walls. This direct contact can be useful for 
care after a liver biopsy has been obtained. After the 
procedure, the patient lies over the region where the 
biopsy has been obtained and the weight of the liver 
stems any localized bleeding. When patients have 
significant ascites, the liver cannot be compressed 
against the walls of the abdomen and blood may pour 
freely into the ascitic fluid. 

The patient has ascites, so another approach for a liver 
biopsy must be considered. 

The patient was referred to the radiology department for 
a transjugular liver biopsy. 

The skin around the jugular vein in the neck was 
anesthetized. Access was obtained through insertion of a 
needle and a guidewire. The guidewire was advanced 
through the right internal jugular vein and into the right 
brachiocephalic vein. It entered the superior vena cava, 
was passed along the posterior wall of the atrium, and 
entered the superior aspect of the inferior vena cava. A 
catheter was inserted over the wire and directed into the 
right hepatic vein. Using a series of dilators, the hole was 
enlarged and a biopsy needle was placed over the wire 
and into the right hepatic vein. The liver was biopsied 
through the right hepatic vein and the biopsy sample 
was removed. A simple suture was used to close the 
internal jugular vein in the neck, and minor compression 
stemmed any blood flow. 

Assuming that the biopsy needle does not penetrate the 
liver capsule, it is not important how much the patient 
bleeds from the liver, because this bleeding will enter 
the hepatic vein and is immediately returned to the 
circulation. 




Abdomen 


Case 4 

HODGKIN'S LYMPHOMA 

A 30-year-old man had a diffuse and poorly defined 
epigastric mass. Further examination revealed 
asymmetrical scrotal enlargement. 

As part of her differential diagnosis, the resident 
considered the possibility that the man had testicular 
cancer with regional abdominal para-aortic nodal 
involvement (the lateral aortic, or lumbar, nodes). 

A primary testicular neoplasm is the most common tumor 
in men between the ages of 25 and 34 and accounts for 
between 1% and 2% of all malignancies in men. A family 
history of testicular cancer and maldescent of the testis 
are strong predisposing factors. 

Spread of the tumor is typically to the lymph node chains 
that drain the testes. 

The testes develop from structures adjacent to the renal 
vessels in the upper abdomen, between the transversalis 
fascia and the peritoneum. They normally migrate 
through the inguinal canals into the scrotum just before 
birth. The testes take with them their arterial supply, their 
venous drainage, their nerve supply, and their lymphatics. 

A computed tomography scan revealed a para-aortic 
lymph node mass in the upper abdomen and enlarged 
lymph nodes throughout the internal and common 
iliac lymph node chains. 

Assuming the scrotal mass was a carcinoma of the testes, 
which would normally drain into the lateral aortic 
(lumbar) nodes in the upper abdomen, it would be very 
unusual for iliac lymphadenopathy to be present. 

Further examination of the scrotal mass was required. 

A transillumination test of the scrotum on the affected 
side was positive. An ultrasound scan revealed normal 
right and left testes and a large fluid collection around 
the right testis. A diagnosis of a right-sided hydrocele 
was made. 

Scrotal masses are common in young males, and 
determining the exact anatomical site of the scrotal mass 


is of utmost clinical importance. Any mass that arises 
from the testis should be investigated to exclude 
testicular cancer. Masses that arise from the epididymis 
and scrotal lesions, such as fluid (hydrocele) or hernias, 
are also clinically important but are not malignant. 

The ultrasound scan revealed fluid surrounding the testis, 
which is diagnostic of a hydrocele. Simple cysts arising 
from and around the epididymis (epididymal cysts) can 
be easily defined. 

A diagnosis of lymphoma was suspected. 

Lymphoma is a malignant disease of lymph nodes. Most 
lymphomas are divided into two specific types, namely 
Hodgkin's lymphoma and non-Hodgkin's lymphoma. If 
caught early the prognosis following radical 
chemotherapy is excellent. 

The patient underwent a biopsy, which was performed 
from the posterior approach. He was placed in the prone 
position in the computed tomography (CT) scanner. A 
fine needle with a special cutting device was used to 
obtain a lymph node sample. A left-sided approach was 
used because the inferior vena cava is on the right side 
and the nodes were in the para-aortic regions (i.e., the 
biopsy needle would have to pass between the inferior 
vena cava and the aorta from a posterior approach, which 
is difficult). The skin was anesthetized using local 
anesthetic at the lateral border of the quadratus 
lumborum muscle. The needle was angled at 
approximately 45° within the quadratus lumborum 
muscle and entered the retroperitoneum to lie beside 
the left-sided para-aortic lymph nodes. Because this 
procedure is performed using CT guidance, the operator 
can advance the needle slowly, taking care not to "hit" 
other retroperitoneal structures. 

A good biopsy was obtained and the diagnosis was 
Hodgkin's lymphoma. The patient underwent 
chemotherapy and 2 years later is in full remission 
and leads an active life. 


412 




Clinical cases • Cose 6 


Case 5 

INGUINAL HERNIA 

A 35-year-old man had a soft mass approximately 
3 cm in diameter in the right scrotum. The diagnosis 
was a right indirect inguinal hernia. 

What were the examination findings? 

The mass was nottender and the physician was not able 
to "get above it." The testes were felt separate from the 
mass, and a transillumination test (in which a bright light 
is placed behind the scrotum and the scrotal sac is 
viewed from the front) was negative. (A positive test 
occurs when the light penetrates through the scrotum.) 

When the patient stood up, a positive cough "impulse" 
was felt within the mass. 


After careful and delicate maneuvering, the mass could 
be massaged into the inguinal canal, so emptying from 
the scrotum. When the massaging hand was removed, 
the mass recurred in the scrotum. 

An indirect inguinal hernia enters the inguinal canal 
through the deep inguinal ring. It passes through the 
inguinal canal to exit through the superficial inguinal ring 
in the aponeurosis of the external oblique muscle. The 
hernia sac lies superior and medial to the pubic tubercle 
and enters into the scrotum within the spermatic cord. 

A direct inguinal hernia passes directly through the 
posterior wall of the inguinal canal. It does not pass down 
the inguinal canal. If large enough, it may pass through 
the superficial inguinal ring and into the scrotum. 


Case 6 

URETERIC STONE 

A 25-year-old man developed severe pain in the left 
lower quadrant of his abdomen. The pain was diffuse 
and relatively constant but did ease for short periods 
of time. On direct questioning the patient indicated 
that the pain was in the inguinal region and radiated 
posteriorly into his left infrascapular region (loin). A 
urine dipstick was positive for blood (hematuria). 

A diagnosis of a ureteric stone (calculus) was made. 

The patient's initial infrascapular pain, which later 
radiated to the left groin, relates to passage of the 
ureteric stone along the ureter. 

The origin of the pain relates to ureteral distention. 

A series of peristaltic waves along the ureter transport 
urine along the length of the ureter from the kidney to 
the bladder. As the ureteric stone obstructs the kidney, 
the ureter becomes distended, resulting in an 
exacerbation of the pain. The peristaltic waves are 
superimposed upon the distention, resulting in 
periods of exacerbation and periods of relief. 

The pain is referred. 

The visceral afferent (sensory) nerve fibers from the ureter 
pass into the spinal cord, entering the first and second 
lumbar segments of the spinal cord. Pain is thus referred 


to cutaneous regions innervated by somatic sensory 
nerves from the same spinal cord levels. 

The patient was investigated by a CT scan. 

Traditionally patients are investigated with a plain 
radiograph to look for the radiopaque stone (90% 
of renal stones are radiopaque). 

An ultrasound scan may be useful to assess for 
pelvicaliceal dilatation and may reveal stones at the 
pelviureteral junction or the vesicoureteric junction. 
Ultrasound is also valuable for assessing other causes of 
obstruction (e.g., tumors at and around the ureteric 
orifices in the bladder). 

Usually an intravenous urogram would be carried out to 
enable assessment of the upper urinary tracts and precise 
location of the stone. 

Not infrequently, CT scans of the abdomen are also 
obtained. These scans not only give information about 
the kidneys, ureters, and bladder but also show the 
position of the stone and other associated pathology. 

If this patient's infrascapular pain was on the right and 
predominantly within the right lower abdomen, 
appendicitis would also have to be excluded. A CT 
scan would enable differentiation of appendicitis and 
urinary colic. 


Abdomen 


Case 7 

INTRAABDOMINAL ABSCESS 

A 27-year-old woman was admitted to the surgical 
ward with appendicitis. She underwent an 
appendectomy. It was noted at operation that the 
appendix had perforated and there was pus within 
the abdominal cavity. The appendix was removed and 
the stump tied. The abdomen was washed out with 
warm saline solution. The patient initially made an 
uneventful recovery, but by day 7 she had become 
unwell, with pain over her right shoulder and spiking 
temperatures. 

This patient had developed an intraabdominal abscess. 

Any operation on the bowel may involve peritoneal 
contamination with fecal contents and fecal flora. This 
may not be appreciated at the time of the operation. 

Over the postoperative period an inflammatory reaction 
ensued and an abscess cavity developed, filling with pus. 
Typically, the observation chart revealed a "swinging" 
pyrexia (fever). 

The most common sites for abscess to develop are the 
pelvis and the hepatorenal recess. 

When a patient is in the supine position, the lowest 
points in the abdominal and pelvic cavities are the 
posterior superior aspect of the peritoneal cavity (the 
hepatorenal recess) and, in women, the recto-uterine 
pouch (pouch of Douglas). 

The shoulder pain suggested that the abscess was in the 
hepatorenal recess and that the pain was referred from 
the diaphragm. 

The motor and sensory innervation of the diaphragm is 
from nerves C3 to C5. The somatic pain sensation from 
the parietal peritoneum covering the undersurface of the 
diaphragm is carried into the spinal cord by the phrenic 
nerve (C3 to C5) and is interpreted by the brain as 
coming from skin over the shoulder—a region supplied 
by other somatic sensory nerves entering the same levels 
of the spinal cord as those from the diaphragm. 

A chest radiograph demonstrated elevation of the right 
hemidiaphragm. 

This elevation of the right hemidiaphragm was due to the 
pus tracking from the hepatorenal space around the 


lateral and anterior aspect of the liver to sit on top of 
the liver in a subphrenic position. An ultrasound scan 
demonstrated this collection of fluid. The abscess cavity 
could be clearly seen by placing the ultrasound probe 
between ribs XI and XII. The inferior border of the right 
lower lobe lies at rib X in the midaxillary line. When the 
probe is placed between ribs XI and XII the ultrasound 
waves pass between the intercostal muscles and the 
parietal pleura laterally on the chest wall, and continue 
through the parietal pleura overlying the diaphragm into 
the cavity of the abscess, which lies below the 
diaphragm. 

Drainage was not by an intercostal route. Instead, using 
CT guidance and local anesthesia, a subcostal drain was 
established and 1 liter of pus was removed (Fig. 4.173). It 
is important to bear in mind that placing a drain through 
the pleural cavity into the abdominal cavity effectively 
allows intraabdominal pus to pass into the thoracic 
cavity, and that this may produce an empyema (pus in 
the pleural space). 

The patient made a slow and uneventful recovery. 



Fig. 4.173 Subphrenic collection of pus and gas. Computed 
tomogram in the axial plane. 


414 




Clinical cases • Cose 8 


Case 8 

COMPLICATIONS OF AN ABDOMINOPERINEAL 
RESECTION 

A 45-year-old man developed a low-grade rectal 
carcinoma just above the anorectal margin. He 
underwent an abdominoperineal resection of the 
tumor and was left with a left lower abdominal 
colostomy (see below). Unfortunately, the man's wife 
left him for a number of reasons, including lack of 
sexual desire. He "turned to drink" and over the 
ensuing years developed cirrhosis. He was brought 
into the emergency room with severe bleeding from 
enlarged veins around his colostomy. An emergency 
transjugular intrahepatic portosystemic shunt was 
created, which stopped all bleeding (Figs 4.174 and 
4.1 75 ). He is now doing well in a rehabilitation 
program. 

A colostomy was necessary because of the low site of the 
tumor. 

Carcinoma of the colon and rectum usually develops in 
older patients, but some people do get tumors early in 
life. Most tumors develop from benign polyps, which 
undergo malignant change. As the malignancy develops 
it invades through the wall of the bowel and then 
metastasizes to local lymphatics. The tumor extends 


Stent- 



Fig. 4.174 Position of a transjugular intrahepatic portosystemic 
shunt stent. Radiograph. 


within the wall for a few centimeters above and below its 
origin. Lymphatic spread is to local and regional lymph 
nodes and then to the pre-aortic lymph node chain. 
These drain eventually into the thoracic duct. 

When this man was assessed for surgery, the tumor was 
so close to the anal margin that resection of the 
sphincters was necessary to be certain that the tumor 
margins were clear. The bowel cannot be joined to the 
anus without sphincters because the patient would be 
fecally incontinent. At surgery the tumor was excised, 
including the locoregional lymph node chains and the 
peritumoral fat around the rectum. 

The free end of the sigmoid colon was brought through a 
hole in the anterior abdominal wall. The bowel was then 
carefully sutured to the anterior abdominal wall to allow 
placement of a bag to collect the feces. This is a 
colostomy. 

Contrary to their usual immediate negative reaction to 
having a bag on the anterior abdominal wall, most 
patients cope extremely well, especially if they have been 
cured of cancer. 



Fig. 4.175 Functioning transjugular intrahepatic portosystemic 
shunt. Venogram. 


(continues) 









Abdomen 


Case 8 (continued) 

This patient's pelvic nerves were damaged. The 
radical pelvic surgical dissection damaged the pelvic 
parasympathetic nerve supply necessary for erection of 
the penis. Unfortunately, this was not well explained to 
the patient, which in some part led to the failure of his 
relationship. With any radical surgery in the pelvis, the 
nerves that supply the penis or clitoris may be damaged, 
so interfering with sexual function. 

This patient was bleeding from stomal varices. 

As he developed a serious drinking problem, his liver 
became cirrhotic and this damaged the normal liver 
architecture. This in turn increased the blood pressure 
in the portal vein (portal hypertension). 

In patients with portal hypertension small anastomoses 
develop between the veins of the portal system and the 
veins of the systemic circulation. These portosystemic 
anastomoses are usually of little consequence; however, 
at the gastroesophageal junction, they lie in a 
submucosal and mucosal position and are subject to 
trauma. Torrential hemorrhage may occur from even 
minor trauma, and death may ensue following blood loss. 
These varices require urgent treatment, which includes 
injecting sclerosant substances, banding, and even 
surgical ligation. 

Fortunately, most of the other portosystemic 
anastomoses are of relatively little consequence. In 
patients with colostomies, small veins may develop 
between the veins of the large bowel (portal system 
drainage) and cutaneous veins on the anterior abdominal 
wall (systemic veins). If these veins become enlarged 
because of portal hypertension, they are subject to 


trauma as feces are passed through the colostomy. 
Torrential hemorrhage may ensue if they are damaged. 

A procedure was carried out to lower the portal pressure. 

To reduce the pressure in the portal vein in this patient, 
several surgical procedures were considered. These 
included sewing the side of the portal vein onto the 
inferior vena cava (portacaval shunt) and sewing the 
splenic vein onto the renal vein (a splenorenal shunt). 
These procedures, however, require a large abdominal 
incision and are extremely complex. As an alternative, it 
was decided to create a transjugular intrahepatic 
portosystemic shunt. 

Creating a transjugular intrahepatic portosystemic 
shunt is a relatively new technique that may be carried 
out under local anesthesia. Using a right internal jugular 
approach, a long needle is placed through the internal 
jugular vein, the superior vena cava, and the right atrium, 
into the inferior vena cava. The right hepatic vein is 
cannulated and, with special steering wires, a needle is 
passed through the hepatic substance directly into the 
right branch of the portal vein. A small balloon is passed 
over the wire and through the hepatic substance and is 
inflated. After the balloon has been removed, a metallic 
stent (a flexible wire tube) is placed across this tract in 
the liver to keep it open. Blood now freely flows from the 
portal vein into the right hepatic vein, creating a 
portosystemic shunt. 

As a result of this procedure, the pressure in this patient's 
portal system is lower and similar to that of the systemic 
venous system, so reducing the potential for bleeding at 
the portosystemic anastomoses (i.e., the colostomy). 


416 




Clinical cases • Cose 9 


Case 9 

CARCINOMA OF THE HEAD OF THE PANCREAS 

A 52-year-old woman visited her family physician 
with complaints of increasing lethargy and vomiting. 
The physician examined her and noted that compared 
to previous visits she had lost significant weight. She 
was also jaundiced, and on examination of the 
abdomen a well-defined 10-cm rounded mass was 
palpable below the liver edge in the right upper 
quadrant (Fig. 4.176). 

The clinical diagnosis was carcinoma of the head of the 
pancreas. 

It is difficult to appreciate how such a precise diagnosis 
can be made clinically when only three clinical signs have 
been described. 

The patient's obstruction was in the distal bile duct. 


Tumor 



Fig. 4.176 Tumor in the head of the pancreas. Computed 
tomogram in the axial plane. 


When a patient has jaundice, the causes are excessive 
breakdown of red blood cells (prehepatic), hepatic failure 
(hepatic jaundice), and posthepatic causes, which include 
obstruction along the length of the biliary tree. 

The patient had a mass in her right upper quadrant that 
was palpable below the liver; this was the gallbladder. 

In healthy individuals, the gallbladder is not palpable. An 
expanded gallbladder indicates obstruction either within 
the cystic duct or below the level of the cystic duct 
insertion (i.e., the bile duct). 

The patient's vomiting was related to the position of the 
tumor. 

It is not uncommon for vomiting and weight loss 
(cachexia) to occur in patients with a malignant disease. 
The head of the pancreas lies within the curve of the 
duodenum, primarily adjacent to the descending part of 
the duodenum. Any tumor mass in the region of the 
head of the pancreas is likely to expand and may encase 
and invade the duodenum. Unfortunately, in this 
patient's case, this happened, producing almost complete 
obstruction. Further discussion with the patient revealed 
that she was vomiting relatively undigested food soon 
after each meal. 

ACT scan demonstrated further complications. 

In the region of the head and neck of the pancreas are 
complex anatomical structures, which may be involved 
with a malignant process. The CT scan confirmed a mass 
in the region of the head of the pancreas, which invaded 
the descending part of the duodenum. The mass 
extended into the neck of the pancreas and had blocked 
the distal part of the bile duct and the pancreatic duct. 
Posteriorly the mass had directly invaded the portal 
venous confluence of the splenic and superior mesenteric 
veins, producing a series of gastric, splenic, and small 
bowel varices. 

This patient underwent palliative chemotherapy, but died 
7 months later. 




Abdomen 


Case 10 

CAVAL OBSTRUCTION 

A 62-year-old man came to the emergency 
department with swelling of both legs and a large left 
varicocele (enlarged and engorged varicose veins 
around the left testis and within the left pampiniform 
plexus of veins). 

The patient was known to have a left renal cell 
carcinoma and was due to have this operated on the 
following week. 

Anatomically it is possible to link all of the findings 
with the renal cell carcinoma by knowing the biology 
of the tumor. 

Renal cell carcinoma tends to grow steadily and 
predictably. Typically, when the tumor is less than 
3 to 4 cm, it remains confined to the kidney. Large 
tumors have the propensity to grow into the renal vein, 
the inferior vena cava and the right atrium and through 
the heart into the pulmonary artery. 

The tumor grew into the renal vein. 

As the tumor grew into the renal vein it blocked off all 
tributaries draining into the vein, the largest of which is 


the left testicular vein. This blockage of the left testicular 
vein caused a dilation of the veins around the left testis 
(a varicocele occurred). 

The swollen legs were accounted for by caval obstruction. 

The tumor grew along the renal vein and into the inferior 
vena cava toward the heart. Renal tumors can grow 
rapidly; in this case the tumor grew rapidly into the 
inferior vena cava, occluding it. This increased the 
pressure in the leg veins, resulting in swelling and pitting 
edema of the ankles. 

The patient unfortunately died on the operating table. 

In this patient's case, a "tongue" of tumor grew into the 
inferior vena cava. At the time of surgery, the initial 
dissection mobilized the kidney on its vascular pedicle; 
however, a large portion of tumor became detached in 
the inferior vena cava. The tumor embolus passed 
through the right atrium and right ventricle and occluded 
the pulmonary artery. This could not be cleared at the 
time of surgery, and the patient succumbed. 


Case 11 

DIVERTICULAR DISEASE 

A 65-year-old businessman came to the emergency 
department with severe lower abdominal pain that 
was predominantly central and left sided. He had pain 
radiating into the left loin, and he also noticed he was 
passing gas and fecal debris as he urinated. 

A CT scan of his abdomen and pelvis was performed 

(Fig. 4.1 77). 

The CT scan demonstrated a collection of fluid (likely a 
pelvic abscess) in the left iliac fossa. Associated with this 
collection of fluid was significant bowel wall thickening of 
the sigmoid colon and multiple small diverticula arising 
throughout the sigmoid colon. Gas was present in the 
bladder. An obstruction was noted in the left ureter and 
the left pelvicalyceal system. 

The patient underwent an urgent operation. 

As the surgeons entered into the abdominal cavity 
through a midline incision, the tissues in the left iliac 



Sigmoid colon diverticuli 


Pelvic abscess 

Sigmoid colon - 


Fig. 4.177 A computed tomogram, in the axial plane, of the 
pelvis demonstrates a loop of sigmoid colon with numerous 
diverticula and a large abscess in the pelvic cavity. 


418 








Clinical cases • Case 12 



Case 11 (continued) 

fossa were significantly inflamed. The surgeon used his 
hand to mobilize the sigmoid colon and entered a cavity 
from which there was a "whoosh" of pus as indicated on 
the CT scan. The pus was washed out and drained. The 
sigmoid colon was remarkably thickened and inflamed 
and stuck to the dome of the bladder. Careful finger 
dissection revealed a small perforation in the dome of the 
bladder, allowing the passage of fecal material and gas 
into the bladder and producing the patient's symptoms 
of pneumaturia and fecaluria. The sigmoid colon was 
resected. The rectal stump was oversewn and the 
descending colon was passed through the anterior 
abdominal wall to form a colostomy. The bladder was 
catheterized and the small hole in the dome of the 
bladder was oversewn. 

The patient had a difficult postoperative period in the 
intensive care unit where he remained pyrexial and 
septic. The colostomy began to function well. 

An ultrasound was performed and demonstrated the 
continued dilatation in the left kidney, and the patient 
underwent a nephrostomy. 

Under ultrasound guidance a drainage catheter was 
placed into the renal pelvis through the renal cortex on 


the left. A significant amount of pus was drained from 
the renal tract initially; however, after 24 hours urine 
passed freely. 

The likely cause for the obstruction was the inflammation 
around the distal ureter on the left. It is also possible that 
a small ureteric perforation occurred, allowing bacteria to 
enter the urinary tract. 

The patient made a further uneventful recovery with 
resumption of normal renal function and left the hospital. 

On return to the surgeon in the outpatient clinic some 
weeks later, the patient did not wish to continue with his 
colostomy and bag. Further to discussion, surgery was 
planned to "rejoin" the patient. 

At operation the colostomy was "taken down" and the 
rectal stump was identified. There was, however, a 
significant gap between the bowel ends. To enable the 
bowel to be sutured, the descending colon was 
mobilized from the posterior abdominal wall. An 
anastomosis was performed and the patient left the 
hospital 1 week later and currently remains well. 


Case 12 

ENDOLEAK AFTER ENDOVASCULAR REPAIR OF 
ABDOMINAL AORTIC ANEURYSM 

A 72-year-old man was brought to the emergency 
department with an abdominal aortic aneurysm (an 
expansion of the infrarenal abdominal aorta). The 
aneurysm measured 10 cm, and after discussion with 
the patient it was scheduled for repair. 

The surgical and endovascular treatment options were 
explained to the patient. 

Treatment of abdominal aortic aneurysms has been, for 
many years, an operative procedure where the dilatation 
(ballooning) of the aorta is resected and a graft is sewn 
into position. A modern option is to place a graft to line 
the aneurysm from within the artery (endovascular 
aneurysm repair). In this technique the surgeon dissects 
the femoral artery and makes a small hole in it. The graft 
is compressed within a catheter and the catheter is 
passed through the femoral artery and the iliac arterial 
system into the distal abdominal aorta. The graft can 


then be released inside the aorta, effectively relining it to 
prevent further expansion of the aneurysm. 

Occasionally the relined aneurysm may continue to 
enlarge after the endovascular graft has been placed and 
a cause needs to be identified. 

A Doppler ultrasound investigation of the abdomen and 
a CT scan revealed there was flow between the 
endovascular lining and the wall of the aneurysm. 

The likely sources for this bleeding were assessed. 

The graft usually begins below the level of the renal 
arteries and divides into two limbs that end in the 
common iliac arteries. The aneurysm may continue to be 
fed from any vessels between the graft and the aneurysm 
wall. These vessels can include the lumbar arteries and 
the inferior mesenteric artery. Interestingly, blood usually 
flows from the abdominal aorta into the inferior 
mesenteric artery and the lumbar arteries; however, with 
the changes in flow dynamics with the graft in place, 

(continues) 


419 


Abdomen 


Case 12 (continued) 

blood may flow in the opposite direction through these 
branches, thereby leading to enlargement of the 
aneurysm. 

Blood flow was from the superior mesenteric artery into 
the aneurysm sac. 

Above the level of the graft the superior mesenteric 
artery arises normally. From the right colic and middle 
colic branches a marginal branch around the colon 
anastomoses, in the region of the splenic flexure, with 
marginal branches from the inferior mesenteric artery 


(this can become a hypertrophied vessel known as the 
marginal artery of Drummond). In this situation, blood 
passed retrogradely into the inferior mesenteric artery, 
filling the aneurysm and allowing it to remain 
pressurized and expand. 

The inferior mesenteric artery was ligated 
laparoscopically and the aneurysm failed to expand 
further. Over the ensuing 6 months the aneurysm 
contracted. The patient remains fit and healthy, with 
two small scars in the groin. 


Case 13 

METASTATIC LESIONS IN THE LIVER 

A 44-year-old woman had been recently diagnosed 
with melanoma on the toe and underwent a series 
of investigations. 

Melanoma (properly called malignant melanoma) can be 
an aggressive form of skin cancer that spreads to lymph 
nodes and multiple other organs throughout the body. 
The malignant potential is dependent upon its cellular 
configuration and also the depth of its penetration 
through the skin. 

The patient developed malignant melanoma in the foot, 
which spread to the lymph nodes of the groin. The 
inguinal lymph nodes were resected; however, it was 
noted on follow-up imaging that the patient had 
developed two metastatic lesions within the right lobe 
of the liver. 

Surgeons and physicians considered the possibility of 
removing these lesions. 

A CT scan was performed that demonstrated the lesions 
within segments V and VI of the liver (Fig. 4.178). 

The segmental anatomy of the liver is important because 
it enables the surgical planning for resection. 

The surgery was undertaken and involved identifying 
the portal vein and the confluence of the right and left 
hepatic ducts. The liver was divided in the imaginary 
principal plane of the middle hepatic vein. The main 
hepatic duct and biliary radicals were ligated and the 
right liver was successfully resected. 

The segments remaining included the left lobe of 
the liver. 


The patient underwent a surgical resection of segments 
V, VI, VII, and VIII. The remaining segments included IVa, 
IVb, I, II, and III. It is important to remember that the lobes 
of the liver do not correlate with the hepatic volume. The 
left lobe of the liver contains only segments II and III. The 
right lobe of the liver contains segments IV, V, VI, VII, and 
VIII. Hence, cross-sectional imaging is important when 
planning surgical segmental resection. 



Fig. 4.178 This postcontrast computed tomogram, in the axial 
plane, demonstrates two metastases situated within the right 
lobe of the liver. The left lobe of the liver is clear. The larger 
of the two metastases is situated to the right of the middle 
hepatic vein, which lies in the principal plane of the liver 
dividing the left and right sides of the liver. 


420 







5 


Pelvis and Perineum 


ADDITIONAL LEARNING RESOURCES 
for Chapter 5, Pelvis and Perineum, 
on STUDENT CONSULT 

( ): 


■ Image Library—illustrations of pelvic and perineal 
anatomy, Chapter 5 

■ Self-Assessment—National Board style multiple- 
choice questions, Chapter 5 

■ Short Questions—these are questions requiring 
short responses, Chapter 5 

■ Interactive Surface Anatomy—interactive surface 
animations, Chapter 5 

■ Medical Clinical Case Studies, Chapter 5 
Pelvic kidney 

Varicocele 

■ Clinical Cases, Chapter 5 
Varicocele 

Sciatic nerve compression 
Pelvic kidney 

Left common iliac artery obstruction 
Latrogenic ureteric injury 
Ectopic pregnancy 
Uterine tumor 

Free Online Self-Study Course: Anatomy 
and Embryology 

■ Anatomy modules 18 through 22 

■ Embryology modules 68 through 70 


Conceptual overview 

General description 
Functions 

Contain and support bladder, rectum, anal canal, 
and reproductive tracts 
Anchors the roots of the external genitalia 
Component parts 
Pelvic inlet 
Pelvic walls 
Pelvic outlet 
Pelvic floor 
Pelvic cavity 
Perineum 

Relationship to other regions 
Abdomen 
Lower limb 
Key features 

The pelvic cavity projects posteriorly 
Important structures cross the ureters in the pelvic 
cavity 

The prostate in men and the uterus in women are 
anterior to the rectum 

The perineum is innervated by sacral spinal cord 
segments 

Nerves are related to bone 
Parasympathetic innervation from spinal cord 
levels S2 to S4 controls erection 
Muscles and fascia of the pelvic floor and perineum 
intersect at the perineal body 
The course of the urethra is different in men and 


women 




Regional anatomy 441 

Pelvis 441 

Bones 441 
Joints 446 
Orientation 448 

Differences between men and women 448 
True pelvis 449 
Viscera 460 
Fascia 481 
Peritoneum 481 
Nerves 486 
Blood vessels 495 
Lymphatics 501 
Perineum 502 

Borders and ceiling 502 

Ischio-anal fossae and their anterior recesses 504 
Anal triangle 504 
Urogenital triangle 506 


Somatic nerves 513 

Visceral nerves 515 

Bloodvessels 516 
Veins 516 
Lymphatics 519 

Surface anatomy 520 

Surface anatomy of the pelvis and perineum 520 
Orientation of the pelvis and perineum in the 
anatomical position 520 
How to define the margins of the perineum 520 
Identification of structures in the anal 
triangle 522 

Identification of structures in the urogenital triangle 
of women 523 

Identification of structures in the urogenital triangle 
of men 524 


Clinical cases 527 



Conceptual overview • Functions 


5 


Conceptual overview 

GENERAL DESCRIPTION 

The pelvis and perineum are interrelated regions associ¬ 
ated with the pelvic bones and terminal parts of the verte¬ 
bral column. The pelvis is divided into two regions: 

■ The superior region related to upper parts of the pelvic 
bones and lower lumbar vertebrae is the false pelvis 
(greater pelvis) and is generally considered part of the 
abdomen (Fig. 5.1). 

■ The true pelvis (lesser pelvis) i s related t o the inferior 
parts of the pelvic bones, sacrum, and coccyx, and has 
an inlet and an outlet. 

The bowl-shaped pelvic cavity enclosed by the true 
pelvis consists of the pelvic inlet, walls, and floor. This 
cavity is continuous superiorly with the abdominal cavity 



and contains elements of the urinary, gastrointestinal, and 
reproductive systems. 

The perineum (Fig. 5.1) is inferior to the floor of the 
pelvic cavity; its boundaries form the pelvic outlet. The 
perineum contains the external genitalia and external 
openings of the genitourinary and gastrointestinal systems. 

FUNCTIONS 

Contains and supports the bladder, rectum, 
anal canal, and reproductive tracts 

Within the pelvic cavity, the bladder is positioned anteri¬ 
orly and the rectum posteriorly in the midline. 

As it fills, the bladder expands superiorly into the 
abdomen. It is supported by adjacent elements of the pelvic 
bone and by the pelvic floor. The urethra passes through 
the pelvic floor to the perineum, where, in women, it opens 
externally (Fig. 5.2A) and in men it enters the base of the 
penis (Fig. 5.2B). 

Continuous with the sigmoid colon at the level of verte¬ 
bra Sill, the rectum terminates at the anal canal, which 
penetrates the pelvic floor to open into the perineum. The 
anal canal is angled posteriorly on the rectum. This flexure 
is maintained by muscles of the pelvic floor and is relaxed 
during defecation. A skeletal muscle sphincter is associated 
with the anal canal and the urethra as each passes through 
the pelvic floor. 

The pelvic cavity contains most of the reproductive tract 
in women and part of the reproductive tract in men. 

■ In women, the vagina penetrates the pelvic floor and 
connects with the uterus in the pelvic cavity. The uterus 
is positioned between the rectum and the bladder. A 
uterine (fallopian) tube extends laterally on each side 
toward the pelvic wall to open near the ovary. 

■ In men, the pelvic cavity contains the site of connection 
between the urinary and reproductive tracts. It also con¬ 
tains major glands associated with the reproductive 
system—the prostate and two seminal vesicles. 


Fig. 5.1 Pelvis and perineum. 


423 





























Pelvis and Perineum 


Reproductive system 

Uterine tube 
Ovary 

Uterus 

Vagina 

Urinary system 

Bladder 


Urethra 


A 



Gastrointestinal 

system 

Rectum 


Anal canal 


Anal aperture 


Reproductive system 

Seminal vesicle 
Ductus deferens 


Prostate 
Ejaculatory duct 


B 



Wvii 


Gastrointestinal 

system 

Rectum 


Anal canal 

Anal aperture 

Urinary system 

Bladder 

Urethra 


Fig. 5.2 The pelvis and perineum contain and support terminal parts of the gastrointestinal, urinary, and reproductive systems. A. In women. 
B. In men. 




































Conceptual overview • Functions 


Anchors the roots of the external genitalia 

In both genders, the roots of the external genitalia, the 
clitoris and the penis, are firmly anchored to: 

■ the bony margin of the anterior half of the pelvic outlet, 
and 


■ a thick, fibrous, perineal membrane, which fills the area 
(Fig. 5.3). 

The roots of the external genitalia consist of erectile 
(vascular) tissues and associated skeletal muscles. 



Body of clitoris 


Vaginal orifice 
Urethral orifice 


Ischial 
tuberosity 


Roots of external genitalia 


Perineal membrane 


Gians of clitoris 


Obturator foramen 



Obturator foramen 


Body of penis 


Root of penis 
Gians of penis 


Ischial tuberosity 

Perineal membrane 


A B Opening of urethra 

Fig. 5.3 The perineum contains and anchors the roots of the external genitalia. A. In women. B. In men. 


























Pelvis and Perineum 


COMPONENT PARTS 
Pelvic inlet 

The pelvic inlet is somewhat heart shaped and completely 
ringed by bone (Fig. 5.4). Posteriorly, the inlet is bordered 
by the body of vertebra SI, which projects into the inlet as 
the sacral promontory. On each side of this vertebra, 
wing-like transverse processes called the alae (wings) 
contribute to the margin of the pelvic inlet. Laterally, a 
prominent rim on the pelvic bone continues the boundary 
of the inlet forward to the pubic symphysis, where the two 
pelvic bones are joined in the midline. 

Structures pass between the pelvic cavity and the 
abdomen through the pelvic inlet. 

During childbirth, the fetus passes through the pelvic 
inlet from the abdomen, into which the uterus has 
expanded during pregnancy, and then passes through the 
pelvic outlet. 


Pelvic walls 

The walls of the true pelvis consist predominantly of bone, 
muscle, and ligaments, with the sacrum, coccyx, and infe¬ 
rior half of the pelvic bones forming much of them. 

Two ligaments—the sacrospinous and the sacrotu- 
berous ligaments—are important architectural elements 
of the walls because they link each pelvic bone to the 
sacrum and coccyx (Fig. 5.5A). These ligaments also 
convert two notches on the pelvic bones—the greater and 
lesser sciatic notches—into foramina on the lateral 
pelvic walls. 

Completing the walls are the obturator internus and 
piriformis muscles (Fig. 5.5B), which arise in the pelvis 
and exit through the sciatic foramina to act on the hip 
joint. 



Pelvic inlet 


Sacro-iliac joint 


Anterior superior 
iliac spine 


Ischial spine 


Coccyx 


Ischiopubic ramus 


Pubic symphysis 


Pubic tubercle 


Obturator foramen 
Ischial tuberosity 


Fig. 5.4 Pelvic inlet. 





















Conceptual overview • Component Ports 


5 



Margin of pelvic inlet 


Lesser sciatic foramen 


Obturator foramen 


Anterior superior 
iliac spine 


Greater sciatic foramen 


Pubic tubercle 


Sacrospinous ligament 
Sacrotuberous ligament 


Ischiopubic ramus 


Ischial tuberosity 



Margin of pelvic 


Piriformis muscle 


internus muscle 


B 

Fig. 5.5 Pelvic walls. A. Bones and ligaments of the pelvic walls. B. Muscles of the pelvic walls. 


427 


















Pelvis and Perineum 


Pelvic outlet 

The diamond-shaped pelvic outlet is formed by both bone 
and ligaments (Fig. 5.6). It is limited anteriorly in the 
midline by the pubic symphysis. 

On each side, the inferior margin of the pelvic bone 
projects posteriorly and laterally from the pubic symphysis 


to end in a prominent tuberosity, the ischial tuberosity. 
Together, these elements construct the pubic arch, which 
forms the margin of the anterior half of the pelvic outlet. 
The sacrotuberous ligament continues this margin poste¬ 
riorly from the ischial tuberosity to the coccyx and sacrum. 
The pubic symphysis, ischial tuberosities, and coccyx can 
all be palpated. 


Pubic symphysis 



Acetabulum 


Sacrum 


Ischiopubic ramus 


Sacrotuberous ligament 


Pubic tubercle 
Obturator foramen 


Anterior superior iliac spine 


Ischial tuberosity 


Margin of pelvic outlet 


Coccyx 


Fig. 5.6 Pelvic outlet. 










Conceptual overview • Component Ports 


5 


Pelvic floor 

The pelvic floor, which separates the pelvic cavity from the 
perineum, is formed by muscles and fascia (Fig. 5.7). 

Two levator ani muscles attach peripherally to the 
pelvic walls and join each other at the midline by a connec¬ 
tive tissue raphe. Together they are the largest components 
of the bowl- or funnel-shaped structure known as the 
pelvic diaphragm, which is completed posteriorly by 
the coccygeus muscles. These latter muscles overlie the 
sacrospinous ligaments and pass between the margins of 
the sacrum and the coccyx and a prominent spine on the 
pelvic bone, the ischial spine. 

The pelvic diaphragm forms most of the pelvic floor and 
in its anterior regions contains a U-shaped defect, which is 
associated with elements of the urogenital system. 

The anal canal passes from the pelvis to the perineum 
through a posterior circular orifice in the pelvic diaphragm. 
The pelvic floor is supported anteriorly by: 

■ the perineal membrane, and 

■ muscles in the deep perineal pouch. 

The perineal membrane is a thick, triangular fascial 
sheet that fills the space between the arms of the pubic 


arch, and has a free posterior border (Fig. 5.7). The deep 
perineal pouch is a narrow region superior to the perineal 
membrane. 

The margins of the U-shaped defect in the pelvic dia¬ 
phragm merge into the walls of the associated viscera and 
with muscles in the deep perineal pouch below. 

The vagina and the urethra penetrate the pelvic floor to 
pass from the pelvic cavity to the perineum. 

Pelvic cavity 

The pelvic cavity is lined by peritoneum continuous with 
the peritoneum of the abdominal cavity that drapes 
over the superior aspects of the pelvic viscera, but in most 
regions, does not reach the pelvic floor (Fig. 5.8A). 

The pelvic viscera are located in the midline of the pelvic 
cavity. The bladder is anterior and the rectum is posterior. 
In women, the uterus lies between the bladder and rectum 
(Fig. 5.8B). Other structures, such as vessels and nerves, lie 
deep to the peritoneum in association with the pelvic walls 
and on either side of the pelvic viscera. 


Piriformis muscle 



Deep perineal pouch 


Perineal membrane 

Vaginal orifice 


-Pubococcygeus muscle 


-Puborectalis muscle 


Coccygeus muscle 


Obturator internus muscle 
Levator ani muscle 

-Iliococcygeus muscle- 


Coccyx 


Coccygeus muscle 


Midline raphe 


Urethral orifice 


Fig. 5.7 Pelvic floor. 


429 














Pelvis and Perineum 


430 



Levator ani 


Perineal membrane 
and deep perineal pouch 


B 

Fig. 5.8 Pelvic cavity and peritoneum. A. In men (sagittal section). B. In women (anterior view). 



Aorta 

-Rectum 


Internal iliac artery 
(artery of pelvis) 


Pelvic inlet 


Uterus 


Bladder 


Peritoneum 


External iliac artery 


Perineum 

The perineum lies inferior to the pelvic floor between 
the lower limbs (Fig. 5.9). Its margin is formed by the 
pelvic outlet. An imaginary line between the ischial 
tuberosities divides the perineum into two triangular 
regions. 


■ Anteriorly, the urogenital triangle contains the roots 
of the external genitalia and, in women, the openings 
of the urethra and the vagina (Fig. 5.9A). In men, the 
distal part of the urethra is enclosed by erectile tissues 
and opens at the end of the penis (Fig. 5.9B). 

■ Posteriorly, the anal triangle contains the anal 
aperture. 























Conceptual overview • Component Ports 


5 


A 


Roots of external genitalia (penis) 


B 



Urogenital triangle 


Levator ani 

Roots of external genitalia 
(clitoris) 

Anal aperture 


Anal triangle 


Urethral orifice 
Vaginal orifice 


Perineal membrane 



Urogenital triangle 


Urethral orifice 


Perineal membrane 
Levator ani 

Sacrotuberous ligament 
Anal aperture 


Anal triangle 


Fig. 5.9 Perineum. A. In women. B. In men. 


431 


















Pelvis and Perineum 


R ELAT ION SHIP TO OTHER REGIONS 
Abdomen 

The cavity of the true pelvis is continuous with the abdom¬ 
inal cavity at the pelvic inlet (Fig. 5.10A). All structures 
passing between the pelvic cavity and abdomen, including 
major vessels, nerves, and lymphatics, as well as the 


sigmoid colon and ureters, pass via the inlet. In men, the 
ductus deferens on each side passes through the anterior 
abdominal wall and over the inlet to enter the pelvic cavity. 
In women, ovarian vessels, nerves, and lymphatics pass 
through the inlet to reach the ovaries, which lie on each 
side just inferior to the pelvic inlet. 


Greater sciatic foramen 

Lesser sciatic foramen 


Obturator canal 


Lower limb 


Fig. 5.10 Areas of communication between the true pelvis and other regions. A. Between the true pelvis, abdomen, and lower limb. 



432 












Conceptual overview • Relationship to Other Regions 


5 


Lower limb 

Three apertures in the pelvic wall communicate with the 
lower limb (Fig. 5.10A): 

■ the obturator canal, 

■ the greater sciatic foramen, and 

■ the lesser sciatic foramen. 

The obturator canal forms a passageway between the 
pelvic cavity and the adductor region of the thigh, and is 


formed in the superior aspect of the obturator foramen, 
between bone, a connective tissue membrane, and muscles 
that fill the foramen. 

The lesser sciatic foramen, which lies inferior to the 
pelvic floor, provides communication between the gluteal 
region and the perineum (Fig. 5.1 OB). 

The pelvic cavity also communicates directly with the 
perineum through a small gap between the pubic symphy¬ 
sis and the perineal membrane (Fig. 5.1 OB). 



• Vagina 


•Anus 


Sacrotuberous ligament 


Lesser sciatic foramen 

• Obturator internus muscle 


Sacrospinous ligament 


• Pudendal nerve 

• Internal pudendal vein 
and artery 


Gap between pubic symphysis and perineal membrane 

• Dorsal vein of penis and clitoris 


Orifices in floor 

• Urethra 


Fig. 5.10, cont’d B. Between the perineum and other regions. 


433 










Pelvis and Perineum 


KEY FEATURES 

The pelvic cavity projects posteriorly 

In the anatomical position, the anterior superior iliac 
spines and the superior edge of the pubic symphysis lie in 
the same vertical plane (Fig. 5.11). Consequently, the 
pelvic inlet is angled 50°-60° forward relative to the 


horizontal plane, and the pelvic cavity projects posteriorly 
from the abdominal cavity. 

Meanwhile, the urogenital part of the pelvic outlet (the 
pubic arch) is oriented in a nearly horizontal plane, 
whereas the posterior part of the outlet is positioned more 
vertically. The urogenital triangle of the perineum there¬ 
fore faces inferiorly, while the anal triangle faces more 
posteriorly. 



434 















Conceptual overview • Key Features 


5 


Important structures cross the ureters in the 
pelvic cavity 

The ureters drain the kidneys, course down the posterior 
abdominal wall, and cross the pelvic inlet to enter the pelvic 
cavity. They continue inferiorly along the lateral pelvic wall 
and ultimately connect with the base of the bladder. 


An important structure crosses the ureters in the pelvic 
cavity in both men and women—in women, the uterine 
artery crosses the ureter lateral to the cervix of the uterus 
(Fig. 5.12A), and in men, the ductus deferens crosses over 
the ureter just posterior to the bladder (Fig. 5.12B). 


Internal iliac artery 


Ureter 


Uterine artery 

Pelvic brim 
(pelvic inlet) 

Uterus 


Internal iliac artery 


Ureter 


Ductus deferens 


Fig. 5.12 Structures that cross the ureters in the pelvic cavity. A. In women. B. In men. 


B 




435 



















Pelvis and Perineum 


The prostate in men and the uterus in 
women are anterior to the rectum 

In men, the prostate gland is situated immediately ante¬ 
rior to the rectum, just above the pelvic floor (Fig. 5.13). 
It can be felt by digital palpation during a rectal 
examination. 

In both sexes, the anal canal and the lower rectum also 
can be evaluated during a rectal examination by a clini¬ 
cian. In women, the cervix and lower part of the body of 
the uterus also are palpable. However, these structures 
can more easily be palpated with a bimanual examination 
where the index and middle fingers of a clinician’s hand 
are placed in the vagina and the other hand is placed on 
the lower anterior abdominal wall. The organs are felt 
between the two hands. This bimanual technique can also 
be used to examine the ovaries and uterine tubes. 


The perineum is innervated by sacral spinal 
cord segments 

Dermatomes of the perineum in both men and women are 
from spinal cord levels S3 to S5, except for the anterior 
regions, which tend to be innervated by spinal cord 
level LI by nerves associated with the abdominal wall 
(Fig. 5.14). Dermatomes of L2 to S2 are predominantly in 
the lower limb. 

Most of the skeletal muscles contained in the perineum 
and the pelvic floor, including the external anal sphincter 
and external urethral sphincter, are innervated by spinal 
cord levels S2 to S4. 

Much of the somatic motor and sensory innervation of 
the perineum is provided by the pudendal nerve from spinal 
cord levels S2 to S4. 



Prostate Rectum 


Fig. 5.13 Position of the prostate gland. 




436 














Conceptual overview • Key Features 


5 


Nerves are related to bone 

The pudendal nerve is the major nerve of the perineum 
and is directly associated with the ischial spine of the pelvis 
(Fig. 5.15). On each side of the body, these spines and the 
attached sacrospinous ligaments separate the greater 
sciatic foramina from the lesser sciatic foramina on the 
lateral pelvic wall. 


The pudendal nerve leaves the pelvic cavity through the 
greater sciatic foramen and then immediately enters the 
perineum inferiorly to the pelvic floor by passing around 
the ischial spine and through the lesser sciatic foramen 
(Fig. 5.15). The ischial spine can be palpated transvagi- 
nally in women and is the landmark for administering a 
pudendal nerve block. 



Ischial spine 


Attachment of levator 
ani and coccygeus 
(pelvic floor) 


Sacrospinous ligament 


Pudendal nerve 


Fig. 5.15 Pudendal nerve. 


437 













Pelvis and Perineum 



Parasympathetic innervation from spinal 
cord levels S2 to S4 controls erection 

The parasympathetic innervation from spinal cord levels 
S2 to S4 controls genital erection in both women and men 
(Fig. 5.16). On each side, preganglionic parasympathetic 
nerves leave the anterior rami of the sacral spinal nerves 
and enter the inferior hypogastric plexus (pelvic plexus) 
on the lateral pelvic wall. 


The two inferior hypogastric plexuses are inferior exten¬ 
sions of the abdominal prevertebral plexus that forms 
on the posterior abdominal wall in association with the 
abdominal aorta. Nerves derived from these plexuses pen¬ 
etrate the pelvic floor to innervate the erectile tissues of the 
clitoris in women and the penis in men. 



Pelvic splanchnic nerves 
(from S2 to S4) 


Anal triangle 


Urogenital triangle 

Prostate 

Nerves to erectile tissue 


Hypogastric nerve 


Inferior hypogastric plexus 


Attachment of pelvic floor 
(levator ani and coccygeus) 


438 


Fig. 5.16 Pelvic splanchnic nerves from spinal levels S2 to S4 control erection. 


















Conceptual overview • Key Features 


5 


Muscles and fascia of the pelvic floor and 
perineum intersect at the perineal body 

Structures of the pelvic floor intersect with structures in 
the perineum at the perineal body (Fig. 5.17). This poorly 
defined fibromuscular node lies at the center of the 
perineum, approximately midway between the two ischial 
tuberosities. Converging at the perineal body are: 


■ the levator ani muscles of the pelvic diaphragm, and 

■ muscles in the urogenital and anal triangles of the 
perineum, including the skeletal muscle sphincters 
associated with the urethra, vagina, and anus. 



Bulbospongiosus muscle 

Ischiocavernous muscle 


Superficial transverse 
perineal muscle 


Perineal body 


Levator ani muscle 
External anal sphincter 


Fig. 5.17 Perineal body. 


439 


















Pelvis and Perineum 


The course of the urethra is different in men 
and women 

In women, the urethra is short and passes inferiorly from 
the bladder through the pelvic floor and opens directly into 
the perineum (Fig. 5.18A). 

In men the urethra passes through the prostate before 
coursing through the deep perineal pouch and perineal 
membrane and then becomes enclosed within the erectile 
tissues of the penis before opening at the end of the penis 
(Fig. 5.18B). The penile part of the male urethra has two 
angles: 


■ The more important of these is a fixed angle where the 
urethra bends anteriorly in the root of the penis after 
passing through the perineal membrane. 

■ Another angle occurs distally where the unattached 
part of the penis curves inferiorly—when the penis is 
erect, this second angle disappears. 

It is important to consider the different courses of 
the urethra in men and women when catheterizing 
patients and when evaluating perineal injuries and pelvic 
pathology. 



Bladder 

Urethra 


Fig. 5.18 Course of the urethra. A. In women. B. In men. 



Bladder 


Urethra 


440 















Regional anatomy • Pelvis 


5 


Regional anatomy 

The pelvis is the region of the body surrounded by the 
pelvic bones and the inferior elements of the vertebral 
column. It is divided into two major regions: the superior 
region is the false (greater) pelvis and is part of the abdomi¬ 
nal cavity; the inferior region is the true (lesser) pelvis, 
which encloses the pelvic cavity. 

The bowl-shaped pelvic cavity is continuous above with 
the abdominal cavity. The rim of the pelvic cavity (the 
pelvic inlet) is completely encircled by bone. The pelvic 
floor is a fibromuscular structure separating the pelvic 
cavity above from the perineum below. 

The perineum is inferior to the pelvic floor and its margin 
is formed by the pelvic outlet. The perineum contains: 

■ the terminal openings of the gastrointestinal and 
urinary systems, 

■ the external opening of the reproductive tract, and 

■ the roots of the external genitalia. 

PELVIS 

Bones 

The bones of the pelvis consist of the right and left pelvic 
(hip) bones, the sacrum, and the coccyx. The sacrum artic¬ 
ulates superiorly with vertebra LV at the lumbosacral joint. 
The pelvic bones articulate posteriorly with the sacrum at 
the sacro-iliac joints and with each other anteriorly at the 
pubic symphysis. 

Pelvic bone 

The pelvic bone is irregular in shape and has two major 
parts separated by an oblique line on the medial surface of 
the bone (Fig. 5.19A): 


■ The pelvic bone above this line represents the lateral 
wall of the false pelvis, which is part of the abdominal 
cavity. 

■ The pelvic bone below this line represents the lateral 
wall of the true pelvis, which contains the pelvic cavity. 

The linea terminalis is the lower two-thirds of this line 
and contributes to the margin of the pelvic inlet. 

The lateral surface of the pelvic bone has a large articu¬ 
lar socket, the acetabulum, which, together with the head 
of the femur, forms the hip joint (Fig. 5.19B). 

Inferior to the acetabulum is the large obturator 
foramen, most of which is closed by a flat connective 
tissue membrane, the obturator membrane. A small 
obturator canal remains open superiorly between the 
membrane and adjacent bone, providing a route of com¬ 
munication between the lower limb and the pelvic cavity. 

The posterior margin of the bone is marked by two 
notches separated by the ischial spine: 

■ the greater sciatic notch, and 

■ the lesser sciatic notch. 

The posterior margin terminates inferiorly as the large 

ischial tuberosity. 

The irregular anterior margin of the pelvic bone is 
marked by the anterior superior iliac spine, the ante¬ 
rior inferior iliac spine, and the pubic tubercle. 


441 




Pelvis and Perineum 


Anterior Posterior 




Fig. 5.19 Right pelvic bone. A. Medial view. B. Lateral view. 


442 
































Regional anatomy • Pelvis 


5 


Components of the pelvic bone 

Each pelvic bone is formed by three elements: the ilium, 
pubis, and ischium. At birth, these bones are connected by 
cartilage in the area of the acetabulum; later, at between 
16 and 18 years of age, they fuse into a single bone 
(Fig. 5.20). 

Ilium 

Of the three components of the pelvic bone, the ilium is 
the most superior in position. 

The ilium is separated into upper and lower parts by a 
ridge on the medial surface (Fig. 5.21 A). 

■ Posteriorly, the ridge is sharp and lies immediately supe¬ 
rior to the surface of the bone that articulates with the 
sacrum. This sacral surface has a large L-shaped facet 
for articulating with the sacrum and an expanded, pos¬ 
terior roughened area for the attachment of the strong 
ligaments that support the sacro-iliac joint (Fig. 5.21). 

■ Anteriorly, the ridge separating the upper and lower 
parts of the ilium is rounded and termed the arcuate 
line. 


Ilium 


Pubis 


Fig. 5.20 Ilium, ischium, and pubis. 



Ischium 


Ligament attachments Iliac tuberosity 


Iliac crest 


Tuberculum of iliac crest 




Posterior 
superior 
iliac spine 


Articular surface for sacrum 


Iliac fossa 


Arcuate 

line 

Body of ilium 


Posterior inferior 
iliac spine 


Anterior inferior 
iliac spine 


Superior pubic 
ramus 


Pubic crest 

Body of pubis 


Inferior pubic ramus 
A 


Pubic tubercle 


Body of 
ischium 


Ischial spine 


Lesser sciatic 
notch 


Ischial tuberosity Ischial tuberosity 

Ramus of ischium D 


Inferior pubic 
ramus 


Ramus of ischium 


Gluteal surface 


Obturator 

groove 


Pectineal 

line 


Superior pubic 
ramus 


Anterior superior 
iliac spine 


Fig. 5.21 Components of the pelvic bone. A. Medial surface. B. Lateral surface. 


443 























Pelvis and Perineum 


The arcuate line forms part of the linea terminalis and 
the pelvic brim. 

The portion of the ilium lying interiorly to the arcuate 
line is the pelvic part of the ilium and contributes to the 
wall of the lesser or true pelvis. 

The upper part of the ilium expands to form a flat, fan¬ 
shaped “wing,” which provides bony support for the lower 
abdomen, or false pelvis. This part of the ilium provides 
attachment for muscles functionally associated with the 
lower limb. The anteromedial surface of the wing is concave 
and forms the iliac fossa. The external (gluteal) surface of 
the wing is marked by lines and roughenings and is related 
to the gluteal region of the lower limb (Fig. 5.2IB). 

The entire superior margin of the ilium is thickened to 
form a prominent crest (the iliac crest), which is the site 
of attachment for muscles and fascia of the abdomen, 
back, and lower limb and terminates anteriorly as the 
anterior superior iliac spine and posteriorly as the pos¬ 
terior superior iliac spine. 

A prominent tubercle, the tuberculum of the iliac 
crest, projects laterally near the anterior end of the crest; 
the posterior end of the crest thickens to form the iliac 
tuberosity. 

Inferior to the anterior superior iliac spine of the crest, 
on the anterior margin of the ilium, is a rounded protuber¬ 
ance called the anterior inferior iliac spine. This struc¬ 
ture serves as the point of attachment for the rectus femoris 
muscle of the anterior compartment of the thigh and the 
iliofemoral ligament associated with the hip joint. A less 
prominent posterior inferior iliac spine occurs along 
the posterior border of the sacral surface of the ilium, 
where the bone angles forward to form the superior margin 
of the greater sciatic notch. 


In the clinic 
Bone marrow biopsy 

In certain diseases (e.g., leukemia), a sample of bone 
marrow must be obtained to assess the stage and 
severity of the problem. The iliac crest is often used for 
such bone marrow biopsies. The iliac crest lies close to 
the surface and is easily palpated. 

A bone marrow biopsy is performed by injecting 
anesthetic in the skin and passing a cutting needle 
through the cortical bone of the iliac crest. The 
bone marrow is aspirated and viewed under a 
microscope. Samples of cortical bone can also be 
obtained in this way to provide information about 
bone metabolism. 


Pubis 

The anterior and inferior part of the pelvic bone is the 
pubis (Fig. 5.21). It has a body and two arms (rami). 

■ The body is flattened dorsoventrally and articulates 
with the body of the pubic bone on the other side at the 
pubic symphysis. The body has a rounded pubic crest 
on its superior surface that ends laterally as the promi¬ 
nent pubic tubercle. 

■ The superior pubic ramus projects posterolaterally 
from the body and joins with the ilium and ischium at 
its base, which is positioned toward the acetabulum. The 
sharp superior margin of this triangular surface is 
termed the pecten pubis (pectineal line), which 
forms part of the linea terminalis of the pelvic bone and 
the pelvic inlet. Anteriorly, this line is continuous with 
the pubic crest, which also is part of the linea termi¬ 
nalis and pelvic inlet. The superior pubic ramus is 
marked on its inferior surface by the obturator groove, 
which forms the upper margin of the obturator canal. 

■ The inferior ramus projects laterally and inferiorly to 
join with the ramus of the ischium. 

Ischium 

The ischium is the posterior and inferior part of the pelvic 
bone (Fig. 5.21). It has: 

■ a large body that projects superiorly to join with the 
ilium and the superior ramus of the pubis, and 

■ a ramus that projects anteriorly to join with the inferior 
ramus of the pubis. 

The posterior margin of the bone is marked by a promi¬ 
nent ischial spine that separates the lesser sciatic notch, 
below, from the greater sciatic notch, above. 

The most prominent feature of the ischium is a large 
tuberosity (the ischial tuberosity) on the posteroinferior 
aspect of the bone. This tuberosity is an important site for 
the attachment of lower limb muscles and for supporting 
the body when sitting. 

Sacrum 

The sacrum, which has the appearance of an inverted tri¬ 
angle, is formed by the fusion of the five sacral vertebrae 
(Fig. 5.22). The base of the sacrum articulates with verte¬ 
bra LV, and its apex articulates with the coccyx. Each of the 
lateral surfaces of the bone bears a large L-shaped facet for 
articulation with the ilium of the pelvic bone. Posterior to 
the facet is a large roughened area for the attachment of 
ligaments that support the sacro-iliac joint. The superior 
surface of the sacrum is characterized by the superior 


444 


Regional anatomy • Pelvis 


5 





Articular facet 
for hip bone 


Anterior sacral 
foramina 


Sacrum 


Promontory 


Promontory 


Sacral canal 


Superior 

articular 

process 


Sacral hiatus 
Sacral cornua 

B 


-Posterior sacral 

foramina 


Superior articular 
process 


Coccyx 


Cornua 

Transverse process 


Fig. 5.22 Sacrum and coccyx. A. Anterior view. B. Posterior view. C. Lateral view. 


aspect of the body of vertebra SI and is flanked on each side 
by an expanded wing-like transverse process termed the 
ala. The anterior edge of the vertebral body projects 
forward as the promontory. The anterior surface of the 
sacrum is concave; the posterior surface is convex. Because 
the transverse processes of adjacent sacral vertebrae fuse 
lateral to the position of the intervertebral foramina and 
lateral to the bifurcation of spinal nerves into posterior and 
anterior rami, the posterior and anterior rami of spinal 
nerves SI to S4 emerge from the sacrum through separate 
foramina. There are four pairs of anterior sacral foram¬ 
ina on the anterior surface of the sacrum for anterior rami, 
and four pairs of posterior sacral foramina on the pos¬ 
terior surface for the posterior rami. The sacral canal is a 
continuation of the vertebral canal that terminates as the 
sacral hiatus. 


Coccyx 

The small terminal part of the vertebral column is the 
coccyx, which consists of four fused coccygeal vertebrae 
(Fig. 5.22) and, like the sacrum, has the shape of an 
inverted triangle. The base of the coccyx is directed supe¬ 
riorly. The superior surface bears a facet for articulation 
with the sacrum and two horns, or cornua, one on each 
side, that project upward to articulate or fuse with similar 
downward-projecting cornua from the sacrum. These pro¬ 
cesses are modified superior and inferior articular pro¬ 
cesses that are present on other vertebrae. Each lateral 
surface of the coccyx has a small rudimentary transverse 
process, extending from the first coccygeal vertebra. Verte¬ 
bral arches are absent from coccygeal vertebrae; therefore 
no bony vertebral canal is present in the coccyx. 445 
































Pelvis and Perineum 


In the clinic 
Pelvic fracture 

The pelvis can be viewed as a series of anatomical rings. 
There are three bony rings and four fibro-osseous rings. 
The major bony pelvic ring consists of parts of the 
sacrum, ilium, and pubis, which forms the pelvic inlet. 
Two smaller subsidiary rings are the obturator foramina. 
The greater and lesser sciatic foramina formed by the 
greater and lesser sciatic notches and the sacrospinous 
and sacrotuberous ligaments form the four fibro- 
osseous rings. The rings, which are predominantly bony 
(i.e., the pelvic inlet and the obturator foramina), are 
brittle rings. It is not possible to break one side of the 
ring without breaking the other side of the ring, which 
in clinical terms means that if a fracture is demonstrated 
on one side, a second fracture should always be 
suspected. 

Fractures of the pelvis may occur in isolation; 
however, they usually occur in trauma patients and 
warrant special mention. 

Owing to the large bony surfaces of the pelvis, a 
fracture produces an area of bone that can bleed 
significantly. A large hematoma may be produced, which 
can compress organs such as the bladder and the ureters. 
This blood loss may occur rapidly, reducing the 
circulating blood volume and, unless this is replaced, the 
patient will become hypovolemic and shock will develop. 

Pelvic fractures may also disrupt the contents of the 
pelvis, leading to urethral disruption, potential bowel 
rupture, and nerve damage. 


Joints 

Lumbosacral joints 

The sacrum articulates superiorly with the lumbar part of 
the vertebral column. The lumbosacral joints are formed 
between vertebra LV and the sacrum and consist of: 

■ the two zygapophysial joints, which occur between 
adjacent inferior and superior articular processes, and 

■ an intervertebral disc that joins the bodies of vertebrae 
LVand SI (Fig. 5.23A). 

These joints are similar to those between other verte¬ 
brae, with the exception that the sacrum is angled posteri¬ 
orly on vertebra LV. As a result, the anterior part of the 
intervertebral disc between the two bones is thicker than 
the posterior part. 

The lumbosacral joints are reinforced by strong iliolum¬ 
bar and lumbosacral ligaments that extend from the 
expanded transverse processes of vertebra LV to the ilium 
and the sacrum, respectively (Fig. 5.23B). 

Sacro-iliac joints 

The sacro-iliac joints transmit forces from the lower limbs 
to the vertebral column. They are synovial joints between 
the L-shaped articular facets on the lateral surfaces of the 
sacrum and similar facets on the iliac parts of the pelvic 
bones (Fig. 5.24A). The joint surfaces have an irregular 
contour and interlock to resist movement. The joints often 




Anterior longitudinal 
ligament 

Iliolumbar ligament 


Ilium 


Lumbosacral 

ligament 


Intervertebral 

disc 


Anterior longitudinal ligament 


Intervertebral 
foramen for 
L5 nerve 


Zygapophysial 

joint 


For posterior 

sacro-iliac 

ligament 


Promontory 


For interosseous 
sacro-iliac ligament 


Anterior sacro-iliac 
ligament 


Intervertebral disc 


Fig. 5.23 Lumbosacral joints and associated ligaments. A. Lateral view. B. Anterior view. 














Regional anatomy • Pelvis 


5 


Sacrum 



Articular surface 


Interosseous sacro-iliac 
ligament (cut) 


Posterior sacro-iliac 
ligament (cut) 



Anterior sacro-iliac 
ligament 


Pubic symphysis 



Interosseous sacro-iliac ligament 


Posterior sacro-iliac ligament overlying 
interosseous sacro-iliac ligament 


Fig. 5.24 Sacro-iliac joints and associated ligaments. A. Lateral view. B. Anterior view. C. Posterior view. 


become fibrous with age and may become completely 
ossified. 

Each sacro-iliac joint is stabilized by three ligaments: 

■ the anterior sacro-iliac ligament, which is a thicken¬ 
ing of the fibrous membrane of the joint capsule and 
runs anteriorly and inferiorly to the joint (Fig. 5.24B); 

■ the interosseous sacro-iliac ligament, which is 
the largest, strongest ligament of the three, and is 


positioned immediately posterosuperior to the joint and 
attaches to adjacent expansive roughened areas on the 
ilium and sacrum, thereby filling the gap between the 
two bones (Fig. 5.24A,C); and 
■ the posterior sacro-iliac ligament, which covers the 
interosseous sacro-iliac ligament (Fig. 5.24C). 


447 












Pelvis and Perineum 


Pubic symphysis joint 

The pubic symphysis lies anteriorly between the adjacent 
surfaces of the pubic bones (Fig. 5.25). Each of the joint’s 
surfaces is covered by hyaline cartilage and is linked across 
the midline to adjacent surfaces by fibrocartilage. The joint 
is surrounded by interwoven layers of collagen fibers and 
the two major ligaments associated with it are: 

■ the superior pubic ligament, located above the 
joint, and 

■ the inferior pubic ligament, located below it. 


In the clinic 

Common problems with the sacro-iliac joints 

The sacro-iliac joints have both fibrous and synovial 
components, and as with many weight-bearing joints, 
degenerative changes may occur and cause pain and 
discomfort in the sacro-iliac region. In addition, 
disorders associated with the major histocompatibility 
complex antigen HLA-B27, such as rheumatoid arthritis, 
psoriasis, and inflammatory bowel disease, can produce 
specific inflammatory changes within these joints. 


Orientation 

In the anatomical position, the pelvis is oriented so that the 
front edge of the top of the pubic symphysis and the 
anterior superior iliac spines fie in the same vertical plane 
(Fig. 5.26). As a consequence, the pelvic inlet, which marks 
the entrance to the pelvic cavity, is tilted to face anteriorly, 
and the bodies of the pubic bones and the pubic arch are 
positioned in a nearly horizontal plane facing the ground. 

Differences between men and women 

The pel vises of women and men differ in a number of ways, 
many of which have to do with the passing of a baby 
through a woman’s pelvic cavity during childbirth. 

The pelvic inlet in women is circular (Fig. 5.2 7A) com¬ 
pared with the heart-shaped pelvic inlet (Fig. 5.2 7B) in 
men. The more circular shape is partly caused by the 
less distinct promontory and broader alae in women. 

■ The angle formed by the two arms of the pubic arch 
is larger in women (80°-85°) than it is in men 
(50°-60°). 

■ The ischial spines generally do not project as far medi¬ 
ally into the pelvic cavity in women as they do in men. 


Pectineal line 



Anterior superior iliac spine 























Regional anatomy • Pelvis 


5 


Prominent medially- 

projecting ischial spines 


-Prominent projecting 

promontory 



Fig. 5.27 Structure of the bony pelvis. A. In women. B. In men. The angle formed by the pubic arch can be approximated by the angle 
between the thumb and index finger for women and the angle between the index finger and middle finger for men as shown in the insets. 


True pelvis 

The true pelvis is cylindrical and has an inlet, a wall, and 
an outlet. The inlet is open, whereas the pelvic floor closes 
the outlet and separates the pelvic cavity, above, from the 
perineum, below. 

Pelvic inlet 

The pelvic inlet is the circular opening between the abdom¬ 
inal cavity and the pelvic cavity through which structures 
traverse between the abdomen and pelvic cavity It is com¬ 
pletely surrounded by bones and joints (Fig. 5.28). The 
promontory of the sacrum protrudes into the inlet, forming 
its posterior margin in the midline. On either side of the 
promontory, the margin is formed by the alae of the 
sacrum. The margin of the pelvic inlet then crosses 
the sacro-iliac joint and continues along the linea termina- 
lis (i.e., the arcuate line, the pecten pubis or pectineal line, 
and the pubic crest) to the pubic symphysis. 


Sacro-iliac joint 


Margin of ala 


Promontory 



Pubic 

tubercle 


Pubic symphysis Pubic Pecten Arcuate 

, crest pubis line 


Linea terminalis 


Fig. 5.28 Pelvic inlet. 


449 



























Pelvis and Perineum 


Pelvic wall 

The walls of the pelvic cavity consist of the sacrum, the 
coccyx, the pelvic bones inferior to the linea terminalis, two 
ligaments, and two muscles. 

Ligaments of the pelvic wall 

The sacrospinous and sacrotuberous ligaments (Fig. 
5.29A) are major components of the lateral pelvic walls 
that help define the apertures between the pelvic cavity 
and adjacent regions through which structures pass. 

■ The smaller of the two, the sacrospinous ligament, is 
triangular, with its apex attached to the ischial spine 
and its base attached to the related margins of the 
sacrum and the coccyx. 

■ The sacrotuberous ligament is also triangular and is 
superficial to the sacrospinous ligament. Its base has a 
broad attachment that extends from the posterior supe¬ 
rior iliac spine of the pelvic bone, along the dorsal aspect 
and the lateral margin of the sacrum, and onto the dor¬ 
solateral surface of the coccyx. Laterally, the apex of the 
ligament is attached to the medial margin of the ischial 
tuberosity. 


These ligaments stabilize the sacrum on the pelvic bones 
by resisting the upward tilting of the inferior aspect of 
the sacrum (Fig. 5.29B). They also convert the greater 
and lesser sciatic notches of the pelvic bone into foramina 
(Fig. 5.29A.B). 

■ The greater sciatic foramen lies superior t o the sacro¬ 
spinous ligament and the ischial spine. 

■ The lesser sciatic foramen lies inferior to the ischial 
spine and sacrospinous ligament between the sacrospi¬ 
nous and sacrotuberous ligaments. 

Muscles of the pelvic wall 

Two muscles, the obturator internus and the piriformis, 
contribute to the lateral walls of the pelvic cavity. These 
muscles originate in the pelvic cavity but attach peripher¬ 
ally to the femur. 

Obturator internus 

The obturator internus is a flat, fan-shaped muscle that 
originates from the deep surface of the obturator mem¬ 
brane and from associated regions of the pelvic bone that 
surround the obturator foramen (Fig. 5.30 and Table 5.1). 




Greater sciatic foramen 


Ligaments prevent 
upward tilting of 
sacrum 


Weight 


Lesser sciatic foramen 


Vertebral column 


Greater sciatic 
foramen 


Sacrospinous 

ligament 


Sacrospinous 

ligament 

Sacrotuberous 

ligament 


Obturator canal 


Sacrotuberous 
ligament 

Obturator membrane 


Lesser sciatic 
foramen 


Obturator membrane 


A 


B 


Fig. 5.29 Sacrospinous and sacrotuberous ligaments. A. Medial view of right side of pelvis. B. Function of the ligaments. 

















Regional anatomy • Pelvis 


5 



Fig. 5.30 Obturator internus and piriformis muscles (medial view of right side of pelvis). 


Table 5.1 

Muscles of the pelvic walls 




Muscle 

Origin 

Insertion 

Innervation 

Function 

Obturator 

Anterolateral wall of true 

Medial surface of greater 

Nerve to obturator internus 

Lateral rotation of the extended 

internus 

pelvis (deep surface of 
obturator membrane and 
surrounding bone) 

trochanter of femur 

L5, SI 

hip joint; abduction of flexed hip 

Piriformis 

Anterior surface of sacrum 
between anterior sacral 
foramina 

Medial side of superior border 
of greater trochanter of femur 

Branches from SI, and S2 

Lateral rotation of the extended 
hip joint; abduction of flexed hip 


The muscle fibers of the obturator internus converge to 
form a tendon that leaves the pelvic cavity through the 
lesser sciatic foramen, makes a 90° bend around the 
ischium between the ischial spine and ischial tuberosity, 
and then passes posterior to the hip joint to insert on the 
greater trochanter of the femur. 

The obturator internus forms a large part of the antero¬ 
lateral wall of the pelvic cavity. 

Piriformis 

The piriformis is triangular and originates in the bridges of 
bone between the four anterior sacral foramina. It passes 


laterally through the greater sciatic foramen, crosses the 
posterosuperior aspect of the hip joint, and inserts on 
the greater trochanter of the femur above the insertion of 
the obturator internus muscle (Fig. 5.30 and Table 5.1). 

A large part of the posterolateral wall of the pelvic 
cavity is formed by the piriformis. In addition, this muscle 
separates the greater sciatic foramen into two regions, one 
above the muscle and one below. Vessels and nerves cours¬ 
ing between the pelvic cavity and the gluteal region pass 
through these two regions. 


451 










Pelvis and Perineum 


Apertures in the pelvic wall 

Each lateral pelvic wall has three major apertures through 
which structures pass between the pelvic cavity and other 
regions: 

■ the obturator canal, 

■ the greater sciatic foramen, and 

■ the lesser sciatic foramen. 

Obturator canal 

At the top of the obturator foramen is the obturator canal, 
which is bordered by the obturator membrane, the 
associated obturator muscles, and the superior pubic 
ramus (Fig. 5.31). The obturator nerve and vessels pass 
from the pelvic cavity to the thigh through this canal. 

Greater sciatic foramen 

The greater sciatic foramen is a major route of communi¬ 
cation between the pelvic cavity and the lower limb 
(Fig. 5.31). It is formed by the greater sciatic notch in the 


pelvic bone, the sacrotuberous and the sacrospinous liga¬ 
ments, and the spine of the ischium. 

The piriformis muscle passes through the greater sciatic 
foramen, dividing it into two parts. 

■ The superior gluteal nerves and vessels pass through the 
foramen above the piriformis. 

■ Passing through the foramen below the piriformis are 
the inferior gluteal nerves and vessels, the sciatic nerve, 
the pudendal nerve, the internal pudendal vessels, the 
posterior femoral cutaneous nerves, and the nerves to 
the obturator internus and quadratus femoris muscles. 

Lesser sciatic foramen 

The lesser sciatic foramen is formed by the lesser sciatic 
notch of the pelvic bone, the ischial spine, the sacrospinous 
ligament, and the sacrotuberous ligament (Fig. 5.31). 
The tendon of the obturator internus muscle passes 
through this foramen to enter the gluteal region of the 
lower limb. 



Superior gluteal nerve -. 

and vessels 

Greater sciatic foramen, 
above and below 
piriformis muscle 


Sciatic nerve, inferior gluteal, - 
posterior femoral cutaneous, 
and quadratus femoris nerves 
and vessels 


Pudendal nerve and internal - 

pudendal vessels and nerve 

to obturator internus Lesser scia ' tic foramen 

Obturator internus muscle -1 


Obturator canal - obturator nerve and vessels 


Fig. 5.31 Apertures in the pelvic wall. 


452 

















Regional anatomy • Pelvis 


5 


Because the lesser sciatic foramen is positioned below 
the attachment of the pelvic floor, it acts as a route of com¬ 
munication between the perineum and the gluteal region. 
The pudendal nerve and internal pudendal vessels pass 
between the pelvic cavity (above the pelvic floor) and the 
perineum (below the pelvic floor), by first passing out of the 
pelvic cavity through the greater sciatic foramen and then 
looping around the ischial spine and sacrospinous liga¬ 
ment to pass through the lesser sciatic foramen to enter the 
perineum. 

Pelvic outlet 

The pelvic outlet is diamond shaped, with the anterior 
part of the diamond defined predominantly by bone and 
the posterior part mainly by ligaments (Fig. 5.32). In the 


midline anteriorly, the boundary of the pelvic outlet is the 
pubic symphysis. Extending laterally and posteriorly, the 
boundary on each side is the inferior border of the body of 
the pubis, the inferior ramus of the pubis, the ramus of the 
ischium, and the ischial tuberosity. Together, the elements 
on both sides form the pubic arch. 

From the ischial tuberosities, the boundaries continue 
posteriorly and medially along the sacrotuberous ligament 
on both sides to the coccyx. 

Terminal parts of the urinary and gastrointestinal tracts 
and the vagina pass through the pelvic outlet. 

The area enclosed by the boundaries of the pelvic outlet 
and below the pelvic floor is the perineum. 


Pubic symphysis 



Pubic arch 


Body of pubis 


Sacrotuberous ligament 


Coccyx 


Ischial tuberosity 


Fig. 5.32 Pelvic outlet. 


453 









454 


Pelvis and Perineum 


In the clinic 

Pelvic measurements in obstetrics 

Transverse and sagittal measurements of a woman's pelvic 
inlet and outlet can help in predicting the likelihood of a 
successful vaginal delivery. These measurements include: 

■ the sagittal inlet (between the promontory and the 
top of the pubic symphysis), 

■ the maximum transverse diameter of the inlet, 

■ the bispinous outlet (the distance between ischial 
spines), and 

■ the sagittal outlet (the distance between the tip of 
the coccyx and the inferior margin of the pubic 
symphysis). 

These measurements can be obtained using magnetic 
resonance imaging, which carries no radiation risk for the 
fetus or mother (Fig. 5.33). 



Arms 


Torso 


Legs 


Pubic symphysis 


Placenta 


Sacral promontory 


Bladder 


Amniotic fluid 


Fig. 533 Sagittal T2-weighted magnetic resonance image of 
the lower abdomen and pelvis of a pregnant woman. 


Pelvic floor 

The pelvic floor is formed by the pelvic diaphragm and, in 
the anterior midline, the perineal membrane and the 
muscles in the deep perineal pouch. The pelvic diaphragm 
is formed by the levator ani and the coccygeus muscles 
from both sides. The pelvic floor separates the pelvic cavity, 
above, from the perineum, below. 

The pelvic diaphragm 

The pelvic diaphragm is the muscular part of the pelvic 
floor. Shaped like a bowl or funnel and attached superiorly 
to the pelvic walls, it consists of the levator ani and the 
coccygeus muscles (Fig. 5.34 and Table 5.2). 

The pelvic diaphragm’s circular line of attachment to 
the cylindrical pelvic wall passes, on each side, between the 
greater sciatic foramen and the lesser sciatic foramen. 
Thus: 

■ the greater sciatic foramen is situated above the level of 
the pelvic floor and is a route of communication between 


the pelvic cavity and the gluteal region of the lower 
limb; and 

■ the lesser sciatic foramen is situated below the pelvic 
floor, providing a route of communication between the 
gluteal region of the lower limb and the perineum. 

Levator ani 

The two levator ani muscles originate from each side of the 
pelvic wall, course medially and inferiorly, and join together 
in the midline. The attachment to the pelvic wall follows 
the circular contour of the wall and includes: 

■ the posterior aspect of the body of the pubic bone, 

■ a linear thickening called the tendinous arch, in the 
fascia covering the obturator internus muscle, and 

■ the spine of the ischium. 

At the midline, the muscles blend together posterior to 
the vagina in women and around the anal aperture in both 
sexes. Posterior to the anal aperture, the muscles come 






Regional anatomy • Pelvis 


5 



Piriformis 

muscle 


Coccygeus 

muscle 


Anococcygeal 

ligament 


Sacrospinous 
ligament (cut) 

Anal aperture 


Obturator internus muscle 

Tendinous arch 

Obturator canal 


Levator ani — 


lliococcygeus 

muscle 

Pubococcygeus 

muscle 

Puborectalis 

muscle 


Urogenital hiatus 


Fig. 5.34 Pelvic diaphragm. 


Table 5.2 Muscles of the pelvic diaphragm 


Muscle Origin 


Insertion 


Innervation 


Function 


Levator 

ani 


In a line around the pelvic wall 
beginning on the posterior 
aspect of the pubic bone 
and extending across the 
obturator internus muscle as 
a tendinous arch (thickening 
of the obturator internus 
fascia) to the ischial spine 


The anterior part is attached 
to the superior surface of 
the perineal membrane; the 
posterior part meets its 
partner on the other side 
at the perineal body, around 
the anal canal, and along 
the anococcygeal ligament 


Branches direct from the 
anterior ramus of S4, and by 
the inferior rectal branch of 
the pudendal nerve (S2 to S4) 


Contributes to the formation of 
the pelvic floor, which supports 
the pelvic viscera; maintains 
an angle between the rectum 
and anal canal; reinforces the 
external anal sphincter and, in 
women, functions as a vaginal 
sphincter 


Coccygeus 


Ischial spine and pelvic surface Lateral margin of coccyx and 
of the sacrospinous ligament related border of sacrum 


Branches from the anterior 
rami of S3 and S4 


Contributes to the formation of 
the pelvic floor, which suppo ts 
the pelvic viscera; pulls coccyx 
forward after defecation 


455 

















Pelvis and Perineum 


together as a ligament or raphe called the anococcygeal 
ligament (anococcygeal body) and attaches to the 
coccyx. Anteriorly, the muscles are separated by a U-shaped 
defect or gap termed the urogenital hiatus. The margins 
of this hiatus merge with the walls of the associated viscera 
and with muscles in the deep perineal pouch below. The 
hiatus allows the urethra (in both men and women), and 
the vagina (in women), to pass through the pelvic dia¬ 
phragm (Fig. 5.34). 

The levator ani muscles are divided into at least three 
collections of muscle fibers, based on site of origin and 
relationship to viscera in the midline: the pubococcygeus, 
the puborectalis, and the iliococcygeus muscles. 

■ The pubococcygeus originates from the body of the 
pubis and courses posteriorly to attach along the midline 
as far back as the coccyx. This part of the muscle is 
further subdivided on the basis of association with 
structures in the midline into the puboprostaticus 
(levator prostatae), the pubovaginalis, and the 
puboanalis muscles. 

■ A second major collection of muscle fibers, the 
puborectalis portion of the levator ani muscles, origi¬ 
nates, in association with the pubococcygeus muscle, 
from the pubis and passes inferiorly on each side to 
form a sling around the terminal part of the gastroin¬ 
testinal tract. This muscular sling maintains an angle 
or flexure, called the perineal flexure, at the anorectal 
junction. This angle functions as part of the mecha¬ 
nism that keeps the end of the gastrointestinal system 
closed. 

■ The final part of the levator ani muscle is the iliococ¬ 
cygeus. This part of the muscle originates from the 
fascia that covers the obturator internus muscle. It joins 
the same muscle on the other side in the midline to form 
a ligament or raphe that extends from the anal aperture 
to the coccyx. 

The levator ani muscles help support the pelvic viscera 
and maintain closure of the rectum and vagina. They are 
innervated directly by branches from the anterior ramus of 
S4 and by branches of the pudendal nerve (S2 to S4). 


Coccygeus 

The two coccygeus muscles, one on each side, are triangu¬ 
lar and overlie the sacrospinous ligaments; together 
they complete the posterior part of the pelvic diaphragm 
(Fig. 5.34 and Table 5.2). They are attached, by their 
apices, to the tips of the ischial spines and, by their bases, 
to the lateral margins of the coccyx and adjacent margins 
of the sacrum. 

These coccygeus muscles are innervated by branches 
from the anterior rami of S3 and S4 and participate in sup¬ 
porting the posterior aspect of the pelvic floor. 


In the clinic 
Defecation 

At the beginning of defecation, closure of the larynx 
stabilizes the diaphragm and intraabdominal pressure 
is increased by contraction of abdominal wall muscles. 

As defecation proceeds, the puborectalis muscle 
surrounding the anorectal junction relaxes, which 
straightens the anorectal angle. Both the internal and the 
external anal sphincters also relax to allow feces to move 
through the anal canal. Normally, the puborectal sling 
maintains an angle of about 90° between the rectum and 
the anal canal and acts as a "pinch valve" to prevent 
defecation. When the puborectalis muscle relaxes, 
the anorectal angle increases to about 130° to 140°. 

The fatty tissue of the ischio-anal fossa allows for 
changes in the position and size of the anal canal 
and anus during defecation. During evacuation, 
the anorectal junction moves down and back and 
the pelvic floor usually descends slightly. 

During defecation, the circular muscles of the rectal 
wall undergo a wave of contraction to push feces 
toward the anus. As feces emerge from the anus, 
the longitudinal muscles of the rectum and levator ani 
bring the anal canal back up, the feces are expelled, and 
the anus and rectum return to their normal positions. 


456 


Regional anatomy • Pelvis 


5 


The perineal membrane and deep 
perineal pouch 

The perineal membrane is a thick fascial, triangular 
structure attached to the bony framework of the pubic 
arch (Fig. 5.35A). It is oriented in the horizontal plane and 
has a free posterior margin. Anteriorly, there is a small gap 


(blue arrow in Fig. 5.35A) between the membrane and the 
inferior pubic ligament (a ligament associated with the 
pubic symphysis). 

The perineal membrane is related above to a thin space 
called the deep perineal pouch (deep perineal space) 
(Fig. 5.35B), which contains a layer of skeletal muscle and 
various neurovascular elements. 



Perineal membrane 


Ischiopubic ramus 

Obturator foramen 


Pubic symphysis 

Inferior pubic ligament 


Ischial tuberosity 



457 




















Pelvis and Perineum 



Obturator internus muscle 


Coccygeus muscle 
-Sacrospinous ligament 


Anococcygeal ligament 
Levator ani muscle 


Deep perineal pouch 

Perineal membrane 


Root of penis 


Fig. 5.35, cont’d Perineal membrane and deep perineal pouch. C. Medial view. 


The deep perineal pouch is open above and is not sepa¬ 
rated from more superior structures by a distinct layer of 
fascia. The parts of the perineal membrane and structures 
in the deep perineal pouch, enclosed by the urogenital 
hiatus above, therefore contribute to the pelvic floor and 
support elements of the urogenital system in the pelvic 
cavity, even though the perineal membrane and deep peri¬ 
neal pouch are usually considered parts of the perineum. 


The perineal membrane and adjacent pubic arch provide 
attachment for the roots of the external genitalia and the 
muscles associated with them (Fig. 5.35C). 

The urethra penetrates vertically through a circular 
hiatus in the perineal membrane as it passes from the 
pelvic cavity, above, to the perineum, below. In women, the 
vagina also passes through a hiatus in the perineal mem¬ 
brane just posterior to the urethral hiatus. 


458 
















Regional anatomy • Pelvis 


5 


Within the deep perineal pouch, a sheet of skeletal 
muscle functions as a sphincter, mainly for the urethra, 
and as a stabilizer of the posterior edge of the perineal 
membrane (Fig. 5.36 and Table 5.3). 

■ Anteriorly, a group of muscle fibers surround the 
urethra and collectively form the external urethral 
sphincter. 

■ Two additional groups of muscle fibers are associated 
with the urethra and vagina in women. One group 
forms the sphincter urethrovaginalis, which sur¬ 
rounds the urethra and vagina as a unit. The second 
group forms the compressor urethrae, on each side, 
which originate from the ischiopubic rami and meet 
anterior to the urethra. Together with the external 
urethral sphincter, the sphincter urethrovaginalis and 
compressor urethrae facilitate closing of the urethra. 

■ In both men and women, a deep transverse perineal 
muscle on each side parallels the free margin of the 
perineal membrane and joins with its partner at the 
midline. These muscles are thought to stabilize the posi¬ 
tion of the perineal body, which is a midline structure 
along the posterior edge of the perineal membrane. 

Perineal body 

The perineal body is an ill-defined but important connective 
tissue structure into which muscles of the pelvic floor and 


Opening for urethra Opening for vagina 



A 


Sphincter 

urethrovaginalis 


Compressor urethrae 
Deep perineal pouch 


Perineal membrane 


Opening for urethra 



Fig. 5.36 Muscles in the deep perineal pouch. A. In women. 
B. In men. 


Table 5.3 Muscles within the deep perineal pouch 


Muscle Origin 


Insertion 


Innervation Function 


External urethral 
sphincter 


Deep transverse 
perineal 


From the inferior ramus 
of the pubis on each side 
and adjacent walls of the 
deep perineal pouch 

Medial aspect of ischial 
ramus 


Surrounds membranous part 
of urethra 


Perineal branches of the 
pudendal nerve (S2 to S4) 


Perineal branches of the 
pudendal nerve (S2 to S4) 


Compresses the membranous 
urethra; relaxes during 
micturition 

Stabilizes the position of the 
perineal body 


Perineal body 


Compressor urethrae Ischiopubic ramus on 
(in women only) each side 


Blends with partner on other 
side anterior to the urethra 


Perineal branches of the 
pudendal nerve (S2 to S4) 


Functions as an accessory 
sphincter of the urethra 


Sphincter Perineal body 

urethrovaginalis 

(in women only) 


Passes forward lateral to the 
vagina to blend with partner 
on other side anterior to the 
urethra 


Perineal branches of the 
pudendal nerve (S2 to S4) 


Functions as an accessory 
sphincter of the urethra 
(also may facilitate closing 
the vagina) 


459 















460 


Pelvis and Perineum 


the perineum attach (Fig. 5.37). It is positioned in the 
midline along the posterior border of the perineal mem¬ 
brane, to which it attaches. The posterior end of the urogeni¬ 
tal hiatus in the levator ani muscles is also connected to it. 

The deep transverse perineal muscles intersect at the 
perineal body; in women, the sphincter urethrovaginalis 
also attaches to the perineal body. Other muscles that 
connect to the perineal body include the external anal 
sphincter, the superficial transverse perineal muscles, and 
the bulbospongiosus muscles of the perineum. 

In the clinic 

Episiotomy 

During childbirth the perineal body may be stretched 
and torn. Traditionally it was felt that if a perineal tear is 
likely, the obstetrician may proceed with an episiotomy. 
This is a procedure in which an incision is made in the 
perineal body to allow the head of the fetus to pass 
through the vagina. There are two types of 
episiotomies: a median episiotomy cuts through the 
perineal body, while a mediolateral episiotomy is an 
incision 45° from the midline. The maternal benefits of 
this procedure have been thought to be less traumatic 
to the perineum and to result in decreased pelvic floor 
dysfunction after childbirth. However, more recent 
evidence suggests that an episiotomy should not be 
performed routinely. Review of data has failed to show 
a decrease in pelvic floor damage with routine use of 
episiotomies. 

Viscera 

The pelvic viscera include parts of the gastrointestinal 
system, the urinary system, and the reproductive system. 


Perineal body 



Fig. 5.37 Perineal body. 


The viscera are arranged in the midline, from front to back; 
the neurovascular supply is through branches that pass 
medially from vessels and nerves associated with the pelvic 
walls. 

Gastrointestinal system 

Pelvic parts of the gastrointestinal system consist mainly of 
the rectum and the anal canal, although the terminal part 
of the sigmoid colon is also in the pelvic cavity (Fig. 5.38). 

Rectum 

The rectum is continuous; 

■ above, with the sigmoid colon at about the level of ver¬ 
tebra Sill, and 

■ below, with the anal canal as this structure penetrates 
the pelvic floor and passes through the perineum to end 
as the anus. 

The rectum, the most posterior element of the pelvic 
viscera, is immediately anterior to, and follows the concave 
contour of the sacrum. 

The anorectal junction is pulled forward (perineal 
flexure) by the action of the puborectalis part of the levator 
ani muscle, so the anal canal moves in a posterior direction 
as it passes inferiorly through the pelvic floor. 

In addition to conforming to the general curvature of 
the sacrum in the anteroposterior plane, the rectum has 
three lateral curvatures; the upper and lower curvatures to 
the right and the middle curvature to the left. The lower 
part of the rectum is expanded to form the rectal ampulla. 
Finally, unlike the colon, the rectum lacks distinct taeniae 
coli muscles, omental appendices, and sacculations 
(haustra of the colon). 

Anal canal 

The anal canal begins at the terminal end of the rectal 
ampulla where it narrows at the pelvic floor. It terminates 
as the anus after passing through the perineum. As it 
passes through the pelvic floor, the anal canal is sur¬ 
rounded along its entire length by the internal and exter¬ 
nal anal sphincters, which normally keep it closed. 

The lining of the anal canal bears a number of charac¬ 
teristic structural features that reflect the approximate 
position of the anococcygeal membrane in the fetus (which 
closes the terminal end of the developing gastrointestinal 
system in the fetus) and the transition from gastrointesti¬ 
nal mucosa to skin in the adult (Fig. 5.38B). 

■ The upper part of the anal canal is lined by mucosa 
similar to that lining the rectum and is distinguished by 
a number of longitudinally oriented folds known as 







Regional anatomy • Pelvis 


5 


A 



Sigmoid colon 


Rectum 


Rectal ampulla 


Anal canal 


Puborectalis muscle 


External anal 
sphincter 


Rectum 



Levator ani — 


lliococcygeus 

Puborectalis 


Internal anal sphincter 
(smooth muscle) 

Pectinate line 


Anocutaneous line 
(“white”) 


Anal column 
Anal sinus 
Anal valve 


Deep 

Superficial 

Subcutaneous 


B 


Anal pecten Anal aperture 


External anal 
sphincter 
(skeletal muscle) 


Fig. 5.38 Rectum and anal canal. A. Left pelvic bone removed. B. Longitudinal section. 


461 



























Pelvis and Perineum 


anal columns, which are united interiorly by crescen¬ 
tic folds termed anal valves. Superior to each valve is 
a depression termed an anal sinus. The anal valves 
together form a circle around the anal canal at a 
location known as the pectinate line, which marks 
the approximate position of the anal membrane in 
the fetus. 

■ Inferior to the pectinate line is a transition zone known 
as the anal pecten, which is lined by nonkeratinized 
stratified squamous epithelium. The anal pecten ends 
inferiorly at the anocutaneous line (“white line”), or 
where the lining of the anal canal becomes true skin. 

Given the position of the colon and rectum in the 

abdominopelvic cavity and its proximity to other organs, it 


In the clinic 

Digital rectal examination 

A digital rectal examination (DRE) is performed by 
placing the gloved and lubricated index finger into the 
rectum through the anus. The anal mucosa can be 
palpated for abnormal masses, and in women, the 
posterior wall of the vagina and the cervix can be 
palpated. In men, the prostate can be evaluated for any 
extraneous nodules or masses. 

In many instances the digital rectal examination may 
be followed by proctoscopy or colonoscopy. An 
ultrasound probe may be placed into the rectum to 
assess the gynecological structures in females and the 
prostate in the male before performing a prostatic 
biopsy. 


In the clinic 

Carcinoma of the colon and rectum 

Carcinoma of the colon and rectum (colorectum) is a 
common and often lethal disease. Recent advances in 
surgery, radiotherapy, and chemotherapy have only 
slightly improved 5-year survival rates. 

The biological behavior of tumors of the colon and 
rectum is relatively predictable. Most of the tumors 
develop from benign polyps, some of which undergo 
malignant change. The overall prognosis is related to: 

■ the degree of tumor penetration through the 
bowel wall, 

■ the presence or absence of lymphatic 
dissemination, and 

■ the presence or absence of systemic metastases. 


is extremely important to accurately stage colorectal 
tumors: a tumor in the pelvis, for example, could invade 
the uterus or bladder. Assessing whether spread has 
occurred may involve ultrasound scanning, computed 
tomography, and magnetic resonance imaging. 

Urinary system 

The pelvic parts of the urinary system consist of the termi¬ 
nal parts of the ureters, the bladder, and the proximal part 
of the urethra (Fig. 5.39). 

Ureters 

The ureters enter the pelvic cavity from the abdomen by 
passing through the pelvic inlet. On each side, the ureter 
crosses the pelvic inlet and enters the pelvic cavity in the 
area anterior to the bifurcation of the common iliac artery. 
From this point, it continues along the pelvic wall and floor 
to join the base of the bladder. 

In the pelvis, the ureter is crossed by: 

■ the ductus deferens in men, and 

■ the uterine artery in women. 


External iliac artery 



462 













Regional anatomy • Pelvis 


5 


Bladder 

The bladder is the most anterior element of the pelvic 
viscera. Although it is entirely situated in the pelvic cavity 
when empty, it expands superiorly into the abdominal 
cavity when full (Fig. 5.39). 

The empty bladder is shaped like a three-sided pyramid 
that has tipped over to lie on one of its margins (Fig. 5.40A). 
It has an apex, a base, a superior surface, and two infero- 
lateral surfaces. 

■ The apex of the bladder is directed toward the top of the 
pubic symphysis; a structure known as the median 
umbilical ligament (a remnant of the embryological 
urachus that contributes to the formation of the bladder) 
continues from it superiorly up the anterior abdominal 
wall to the umbilicus. 


■ The base of the bladder is shaped like an inverted tri¬ 
angle and faces posteroinferiorly. The two ureters enter 
the bladder at each of the upper corners of the base, 
and the urethra drains inferiorly from the lower corner 
of the base. Inside, the mucosal lining on the base of the 
bladder is smooth and firmly attached to the underlying 
smooth muscle coat of the wall—unlike elsewhere in the 
bladder where the mucosa is folded and loosely attached 
to the wall. The smooth triangular area between the 
openings of the ureters and urethra on the inside of the 
bladder is known as the trigone (Fig. 5.40B). 

■ The inferolateral surfaces of the bladder are cradled 
between the levator ani muscles of the pelvic diaphragm 
and the adjacent obturator internus muscles above the 
attachment of the pelvic diaphragm. The superior 
surface is slightly domed when the bladder is empty; it 
balloons upward as the bladder fills. 



Trigone 

Superior surface 


Median 

umbilical 


Apex 

Inferolateral 

surfaces 


Urethra 



Fig. 5.40 Bladder. A. Superolateral view. B. The trigone. Anterior view with the anterior part of the bladder cut away. 


463 








Pelvis and Perineum 


Neck of bladder 

The neck of the bladder surrounds the origin of the urethra 
at the point where the two inferolateral surfaces and the 
base intersect. 

The neck is the most inferior part of the bladder and also 
the most “fixed” part. It is anchored into position by a pair 
of tough fibromuscular bands, which connect the neck 
and pelvic part of the urethra to the posteroinferior aspect 
of each pubic bone. 

■ In women, these fibromuscular bands are termed pubo¬ 
vesical lig